In procmail, how can I manipulate a subject line with two MATCH variables?

I am succeeding rewriting my subject line to have a [LIST] prepended to it: :0fhw * ^TO_[^@ ]+@example\.com\> * ^Subject:\/.+ | /usr/local/bin/formail -I"Subject: [LIST]$MATCH" This succeeds and turns:

Subject: here is the subject line

into

Subject: [LIST] here is the subject line

ButeI also want to insert the user portion of user@example.com into the subject line, like this:

Subject: [LIST] user@example.com here is the subject line

... and I don't understand how to do this when I only get one $MATCH variable! How can I insert two different variables into the single formail line that rewrites the subject line?