[APregnantGuy]

I use a cylinder-shaped microbead pillow with a wad of clothes underneath it for size. This goes under an A-shirt (or "wife-beater") two sizes bigger than what I regularly wear. I tuck the "belly" into a pair of spandex/cotton boxers, worn backwards and also two sizes too big, and stretch the boxers over the belly so that they almost touch my chest. After that, I can put on any pants or shirts that I want.

You can see the result of all of this in my profile picture. It leads to a realistic look, but I noticed that it does cause the belly to sit somewhat low.