I also ran into this issue, and dealt with it as suggested here by
changing to sets.  Because I have underlying code that has to deal both
with small hand-crafted regular expressions and arbitrarily-large
machine-generated sets of paths, I subclassed set and implemented the
match and search methods in my subclass so that the underlying code
would work both against the hand-generated regular expressions and the
machine-generated sets of paths.  Hope this helps someone else who runs
into this restriction.