>The only annoyance is that none of the existing Linux distros support this yet as part of their network client integration, so you have to script it yourself around dhclient (see the -P argument), which is a little hairy if you want to get the hooks right (I punted and just did it once manually and left dhclient running).

I think OpenWRT has all you need for this. At least I think that's exactly what I did with my ISP config on my own router just with the LuCi web interface.