If we're talking about the same position then I haven't really been put in that situation any significant number of times, 3 or 4 times max, or remember said position very well so I wouldn't know.
Maybe try rolling to your stomach and when/if he tries to put his hooks in keep rolling through it to get halfguard. But, I'm just spewing out theoretical stuff that probably wouldn't and would get your back taken or mounted if it did.
Or you could try moving to inverted guard like the other guy said, but I would think the top guy would be putting some serious pressure on you which would make contorting in such a way difficult IMHO.
Good question though, got me thinking. Probably ask my instructor tomorrow.