Shorewall users - May 2005 - translation of a SNAT iptables script to the shorewall way

hi list,
any idea how i can transcribe this simple iptables script to shorewall
config? wich files should be modified ? 

iptables  -A POSTROUTING -t nat -s 10.8.0.0/16 -j SNAT --to-source
$SOURCEIP