This isn't directly possible. You'll need to write a shared lib that embeds Perl; you can go from there. It's likely going to be a lot of work though - probably much more than you will want to invest, judging from the fact that you'd prefer to write your PAM module in Perl.
Makeshifts last the longest.
Comment on Re: PERL & PAM (Pluggable Authentication Modules)
It shouldn't be too hard to write a shared lib that makes RPC calls to a server writen in perl, listening on a unix or internet socket, implementing what the shared lib pretends to implement. There are already tons of PAM modules that consult various servers for information.
Alexander
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Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)