I have found some plans for furniture on the internet, but a bit too complicated for the novice.
I think in a pinch a wooden saw horse would suffice. Mamasboy mentioned a 2 x 6 with foam padding and maybe water resistant vinyl, maybe some eye bolts to attach some restraints for the arms and legs, possibly some padded arm rests and leg rests to be able to position the "volunteer" in such a way that the target areas are accessible and able to enjoy hours of fun.
Oh! For enemas, if you don't have ceiling rafters or pulleys and hooks on the ceiling, you might want to add a pole to hang the bag from. Hmmm, maybe some wheels on the legs for ease of proper positioning or lighting angles.
Very interesting ideas... >:D