Well, seeing the sort of things some people can do, I guess that there may be some regexen wizardry to achieve what the OP is after. I'm not really sure, though. And even if possible, I wonder why one should make his like hard like that, except, possibly, for a challange.
Sure - you could for example write your own regexp engine to have different behaviour and patch it in, but I see the set of possible such wizardry as not intersecting with the set of acceptable solutions.