Depends on your platform, but "os-command" will let you execute an external program to do the zipping.
E.g. I use the following to send an email on a unix box:
command="cat tmp.fil | mail -s ""Your PO " + po_nbr + " is stuck""" + " " + usr_mail_address.
os-command silent value(command).
It shouldn't be too hard to call your zip executable.
