Perl is not C or C++ or Java (no function prototypes/signatures), so you can't really write a plugin for doxygen, at least not a very good one. Well, you can, given your code conforms to one style, but if you're going to do that, you might as well use OODoc or ePod instead.

I myself like to use Test::Pod::Coverage to make sure my public apis are documented with good ol pod :)

Actually, I do recall that B::Xref could be very very handy to accomplish something doxyish ... i think i'll suggest that gmpassos and markov consider employing those in their respective thingamajiggers, maybe :)