well, I can imagine at least three ways to do so:

• pipe lsof to your script.
• get lsof source code and wrap it inside an XS or Inline::C module.
• rewrite it completely (or just the parts that you need) in pure Perl translating the C source.

Sometimes the last alternative is surprinsingly easy, for instance Net::SSH::Perl seems to be programmed this way.

update: I have been looking at the original lsof package and it comes with several sample perl scripts that use it. They go with the pipe aproach.