In general, the Regexp engine in perl is not documented to support reentrancy, and from several experiments of my own and others here, I've found plenty to suggest that the code isn't designed to support reentrancy, either.

My biggest experimentation in this area was in developing Pentominos Solving Quine, because using a backtracking position iterator would make complete sense for solving position puzzles. That is, if you could recurse. So instead, I grab and manipulate pos (there's only one) to emulate recursion.