That would be really difficult to do for two reasons:
1. You would need to be laying down in water. Your back would need to be touching a chamois that was on top of aluminum foil so that the electricity would spread throughout your back.
2. You would need another point of contact for the other polarity of electricity, which would need to be separate from the water you are laying in. If you can manage to have your feet in a separate tray of water, then it might be possible, but I doubt it would be effective.
The machine is specialized for delivering specific voltages and amps but using a DC generator would achieve similar results. The padding or applicator is just setup so that current can flow through it. If you connect it to an electrical source, it should be just as effective. Since i've never used that device I cant be certain.
However, I do use a chamois with aluminum foil underneath it to sit on and treat the back of my legs. I can say with 100% certainty that it works on me. This isn't too different from what is being done with that applicator mentioned in your post.
What would I need to buy to do this effectively I've never made one of these before and don't want to mess it up