I think you're out of luck. I don't think there's an easy way to do this.

Perl.com: Maintaining Regular Expressions contains a minor amount of discussion about this. One relevant statement:

Therefore, Regexp::DeferredExecution should only be used with "constant" regular expressions; there is currently no way to overload dynamic, "interpolated" regular expressions.

Of course, whenever I see "no way" in a context like that, I know it means "no easy way"... and, knowing you, you'll manage to figure it out somehow. So, let us know when you do! ;-)

-sauoq
"My two cents aren't worth a dime.";