Above a shaped joint waiting to get a top-coat.
My first experiment....
Materials:
1) Hemp fiber - loose and hemp fabric (optional) or use cord/belt (like at Evolve bikes)
2) West system epoxy - w. fast hardener
3) West systems products like cups and application sticks are useful b/c they are reusable
4) Sander
5) Dremel - with tungsten cutter, tubular sanding disk
6) Respirator w. organic vapor filter (just use it, if you start getting a headache... its brain damage)
7) Spring loaded rubber tipped metal clamps (shown below)
8) Heavy duty rubber gloves (disposables get stuck and rip easily)
9) Perforated roll of electrical tape (take a small drill bit and drill a bunch of holes into it while its on the cardboard roll)
Method:
Take some hemp fiber carefully make a 1 and 1/2" wide strip of it. Keep in mind that you want a consistent layer of this stuff, so make it even. Lightly roll it in your hands to make a very loose rope like product. Although making a tight rope seems appealing it is not. For two reasons, first you want as much overlap between fibers to make a strong bond, and second, with a tighter rope it is difficult to get proper coverage. Wrap one layer of this where you want it and pin it with a clamp. You can also use a glue gun to pin down the end of the rope. Then mix your epoxy and apply until you think you have just saturated the hemp.
The metal clamp... very handy.
You can use a hitch to finish up the end of a rope or you can use it to switch the direction of your wrap.
Above I used a piece of pipe insulation to try to keep epoxy out of the treads of the bottom bracket. Not sure if it worked yet. If I don't come back to complain, assume it worked.NOTE: the pipe insulation worked Ok, not great. Tips for next time. Try rubbing some of your bike grease on the threads first. Then shove some pencils or something into the pipe insulation (try to overstuff it, it will expand a bit into the threads, thus keeping the epoxy out).
It is important to not put too much epoxy (reduced tensile strength) but not too little either. I add epoxy up to the point where compression with my applicator stick pushes up a small amount of epoxy from the surface. Make sure that work it into all the nooks etc. As with many other composite materials (such as reinforced concrete), the two materials act together, each overcoming the deficits of the other. Whereas the plastic resins are strong in compressive loading and relatively weak in tensile strength, the hemp fibers are strong in tension but have no strength against compression. Try a practice one to get a feel for it.
Now to reduce the amount of epoxy and to compress the fiber, wrap the area with the perforated electrical tape (sticky side out). I try to pull as tight as I can without breaking the tape. Wipe off the excess resin as you go. After the tape is applied, I massage the area, in an attempt to work the epoxy deeper into the fibers and to remove any excess. Here's an example. Let it set. Oddly enough the epoxy doesn't stick to the tape too much. Take it off well after the epoxy is no longer sticky to the touch, after 1-1 1/2 hours depending on how hot and dry the area you are working in is (epoxy sets much quicker in high temps). It doesn't matter if you let it set over night either. You will be able to remove it relatively easily. Just make sure to sand it before applying more epoxy.
Here is the first application. The next 2 layers I will concentrate more on the aesthetics. Add more layers progressively until you think you have added too much. 
Now take your dremel and sander/sandpaper and have at it! The mini tubular sanding disks for the dremel work extraordinarily well, to get a very even surface a normal sander comes in handy too. Try them out you will be surprised. It will save about three years of your life. Get one you wont regret it. You can shape the joint down to a nice looking calfee-esk thing in a few minutes. Depending on your likes you might want to add a polish coat of epoxy to clean it up nice. NOTE: If you build the joint out to the waxy part of your poles (the unsanded part) you can easily cut away excess resin with a razor. This allows you to make a nice clean edge between your joint and the bamboo. This sharp edge can then be shaped using your dremel sander.Note: If you want to go with the black joint look on some of the calfee bikes I believe he uses an outer layer of thickened epoxy (404 high-density filler) with graphite additive. See below for more info.
An example of a good sanding job and an ok mitering...
Interpreting Calfee Techniques
Surely the best builder in the field is Calfee. Here are my thoughts. First it looks like he is using a graphite additive here from west systems to get that nice dark look. Second I interpret his use of epoxy here as a plug. You build up the bottom bracket arm so that it is level with your tubes using thickened epoxy (additives from west systems) or using your fiber/epoxy mix. This plug will take most of the force off of the bamboo and put it directly onto the metal arms. Then its just a matter of building it up some more and then sanding the hell out of it until you have a pretty looking thing. From the picture below we can see that you need to think about the shortcomings of bamboo also. Since he is using a disk brake here he knows that additional force will be placed on the chain stay on that side. So he builds out some extra support for it.
Fun projects
It is also possible to make tubes out of this stuff. Here is an experimental head tube. I used pipe insulation as a mold (with wood pole through it to keep it straight). They I applied wetted hemp fabric to make the inside of the tube and then used the loose fiber for the rest. You can set a headset in this thing and Im pretty sure it legit. Although I should say that calfee seems to use alot of metal components.
Attempting to make a seat out of hemp fabric. Planning to treat the canvas cloth like carbon fiber. Multiple layers of canvas layered on at different angles to increase strength.
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