All necessary stuff is available in the systemd overlay.
That's kind of a large patch, perhaps it would be better to push it upstream first.
Created attachment 316915 [details]
f17 dnsmasq service
I took dnsmasq service from f17, its very simple and works good.
Created attachment 316917 [details, diff]
dnsmasq 2.61 ebuild patch
simple ebuild fix, for support dnsmasq.service taken from fedora 17
(In reply to comment #1)
> That's kind of a large patch, perhaps it would be better to push it upstream
Could simple variant taken from F17 be added to portage? pushing upstream could take a lot of time.
The new ebuild for net-dns/dnsmasq-2.63 provided systemd units.