Appending text to subject line

I currently have a procmail recipe that forwards a copy of my e-mail to a second
e-mail address.  I would like to append a short string of text to the subject
line of each forwarded message. My recipe is something like this:

:0c
!secondaddress(_at_)isp(_dot_)com

How would I, for example, add the text "xyz" to the end of the subject line of
the forwarded message?

Thanks,

Tom