a definevar var in indexes

I have something like this running through procmail:

:0:
| /usr/local/bin/mhonarc -add -outdir $MAILDIR/subdir \
  -definevar FOO="$FOO" \
  -rcfile $LIBDIR/mhonarc.rc -quiet -- -

Everything works just fine, except that each time the indexes get
re-created (every time a message comes in), the last message's value
for $FOO$ ends up in the index for every message in the list.  Is there a
per message definevar?

Annotate?  One run of mhonarc to add the msg, a 2nd to add a note for
it?

Thanks,
  Jason