Does anyone have any experience with pushing TMAX 100 to 400 or higher?

I've read plenty that says Tri-X is better at 400, and is much more accepting of push processing, but I'm stuck with TMAX 100 at the moment.

I'm considering this for a couple of reasons.

1. I took 4 shots already, accidentally exposed for 400 ISO. Not a big deal, really.

2. I still have 32 shots left on this roll, in my only 35mm camera, and I want to take it out tomorrow night for some St. Patty's Day shots. If I could swap film I would, but I don't want to waste the whole roll.

I know I will have to use a flash whether it's 100 or 400, but the background will look better at 400...at least that's what I think. I'll be doing flash shots, some with shutter lag, some with no lag, and some as wide open as f2.8.

If anyone has any general suggestions for how to get the most out of this situation (dark bar, TMAX 100), I'm all ears (or eyes, in this case).

Another question: Since my camera automatically selects film speed, and I don't want to carry my hand held meter, can I just set the exposure compensation to under expose by 2 stops and get the same results as changing the film speed from 100 to 400?

Thanks a bunch!

Paul