Okay I finally bit the bullet and got several pairs of tights and wayyy too much polyfill lol. Since I'm not trying to go feminine I really only needed to get the hips/butt/thighs more rounded out, and this process works really well.
I've always felt that I needed some extra on my lower-half to supplement the big belly I make, and this might just be perfect. The layers keep the stuffing from moving too much, and the stuffing holds its shape way better than I thought it would.
The only cons with this setup for me personally are:
1) It gets really hot - even in AC I was sweating after 30min.
2) Even with a base tights layer on, the polyfill was starting to irritate my skin through the tights after 30min or so. I guess the solution is to wear 2 base layers before stuffing instead of 1, but that'd be even warmer.
3) No easy groin access - this isn't THAT big a deal compared to the others, but if you have to pee then you have to take everything off.
Overall though, this method is great. I can't wait to tinker some more with it and take it for a test drive out in public.
*UPDATE*
It's really fun to take out in public. Adding some extra padding between the thighs to force a waddle feels amazing lol. It also feels really good to actually fill out my size 46 pants (I'm a size 34 IRL). The scratchiness from #2 above really didn't happen anymore after the first time or two, but #3 is probably my biggest gripe still. Not being able to go to the bathroom in it really puts a hard time-limit on how long you can be out in it, especially if you drink anything while out. I'm not sure there's a solution for it either, besides some kind of catheter lol. But I'm not that desperate.
4 months