>Not really, expect maybe resync ipf (ipf -y) each time you get an address.
>dhclient should have hooks to run user commands on such events.

cat > /etc/dhclient-exit-hooks << EOF
if [ -n "$new_ip_address" -a "$new_ip_address" != "$old_ip_address" ]; then
	ipf -y
fi
EOF

or thereabouts.

-- 
|-----< "CODE WARRIOR" >-----|
codewarrior@daemon.org             * "ah!  i see you have the internet
twofsonet@graffiti.com (Andrew Brown)                that goes *ping*!"
andrew@crossbar.com       * "information is power -- share the wealth."