Today, I actually tried something out. My brother was at work and has been putting up a couple aquariums (including a huge 6' wide one), and that left a lot of excess tubing lying around, so I started thinking.
It may not be much to the inflation suit makers, but its a simple thing to do. I got a bit of the tubing, a heavy duty garbage, and some of the tubing. I detached the shower head in my shower (mine was simple, I just unscrewed it), and attached the hose to it. Then tucked the garbage bag down my shirt and underwear, and secured the hose in the bag. Simply tying the pull cords around the hose and bag makes I nice tight hold. After that, I let the water loose and the bag filled up, making my belly look SO huge. It felt great and the water's weight made it even better as I tried holding it up. Eventually, the bag burst and water went everywhere, living me in drenched clothes. :D
In the end... I should have double layered the bag and wear something thats a one piece. >_<