Wear an under armour shirt that is a size too small. It will tighten everything up nicely.
I wear XL size shirts and I wear a medium under armor shirt while costuming. Its very tight and probably cuts off circulation but I've trooped for about 5 hours while wearing it and have had no problems.
You want to buy a compression suit.. Basically it's a male girdle. Sort of like long underwear with heavy elastic around the middle, sides and butt. We have used them in creature suit actors to slim them down further then thier regular anatomy. Do a google search and you will find them.. They can be worn comfortably under your pred suit
LMFAO! I think we all have that problem, Unless your like 125lb soak an wet Like me I'm 225 lbs and only 5'8 and Stalky but toned. However in some outfits yes I look like a huge pug the body armor trick works wonders till you pass out!