Can you get a spotter? Maybe some stuff to failure would work for you.
What's your real goal, though? To get a bigger chest, or lift more weight?
Bigger muscles, you could try super-slow sets. There's a Cambodian guy in my gym, he lifts about half the weight I do, but it's slow, careful and with absolutely perfect form - and his muscles are bigger than mine.
More weight, have a chat to a powerlifter. Those guys have all sorts of funky techniques with arching their back and flinging their legs around to get weight up there. Couldn't really describe it easily in words, and anyway I've never done it myself.