Pinning both his arms is just going to make the person being pinned feel stupid, as he pins your arms down with his hands, his ability to submit goes right down the drain. There are still one or two, but they are not likely to work (mostly shoulder to neck stuff.

Anyway, escaping it. I assume your arms are folded up towards your head. Extend your arm until it is straight out to your side so that his arm is now the furthest away form his body it's going to be, then yank back.
If you can get your wrist up then pull away from the thumb. All in all, there isn't much of an escape form this position, because it just isn't a great position. (Often, the better a position is, the more scientifically you can break them apart). Submission power goes way down here, so just avoid it if you don't want to be in it.