Help calling external perl script

I have email forwarded to me from one particular address in which part of 
the header (From: and Subject: )is garbaged into the email message body.  
I've written a small Perl script to re-format and extract these fields.  My 
question:  what's the best way to call this script from Procmail, and use 
these extracted fields?  I've tried this:

:HBhbf
* ^From:(_dot_)*brankin(_at_)wested(_dot_)org
    | ./test.pl

The logfile indicates that the script is being called, but of course 
incoming mail isn't affected.  How do I place the extracted fields into the 
messages?  I would assume I need to pass them as environment variables back 
to procmail...how is that done?

Any info appreciated.

Sincerely,

Brian Rankin