What about sticking the bamboo right into the back lower section of the GS background right at the bottom? They don't have to be in a pool of water and grow just about anywhere. If you angle the holes to get the overhanging effect with the bamboo, it will make places to climb and bamboo only needs a tiny bit of water to grow. In this case, the water source would be the water collected in your drainage layer.

I use to have bamboo in with my WTFs and I just set them into a pile of stones to support them standing upright. I eventually had to remove them though since they are now well over 3 feet high :-)