how implement NAT-PMP on Gentoo home router?

[iMike]

Does anyone have any experience or advice on how one could go about running NAT-PMP (or UPnP) on a home router set up as per http://www.gentoo.org/doc/en/home-router-howto.xml? I set up a such a Gentoo router a few weeks ago, but one of the machines I connect to it is a Mac where it would be nice to use back-to-my-mac (Apple's VNC more or less) and that requires either NAT-PMP or UPnP.

A little searching around and I see portage contains linux-igd and some gupnp stuff. Is that the place to start? Outside of portage, I see something called stallone that could be interesting. And/or, is this a job for iptables? I notice my /etc/service contains nat-pmp as 5351/tcp & udp but the back-to-my-mac supposedly uses UDP port 4500. Strange?

Someone else appears interested in this on the Wiki, but HOWTO_Setup_UPnP_with_IPTables seems to just be a stub right now.

Thanks for any pointers.
/iMike