Whatever you do, DO NOT use "brightness," instead you should use "LEVELS". Crank up gamma, then crush the blacks back to being black (cause increasing gamma will cause the blacks to start washing out). You can also mess with the whites on the levels, but that doesn't work as well. And, yes, this will add GRAIN, but it might make it watchable. I use this technique all of the time when videoing in super-dark clubs. I open the aperature all of the way, and it's still too dark, but in post, you can use levels to squeek out a bit more light (but NEVER use brightness, it'll look like ass).