Sorry, can't answer your question about how/where to duct cool air. However, like a lot of other people, I had the "hot foot" problem too. It's not so much that you need to get cool air in, but need to find out what's causing the hot air and address that. Otherwise, I don't think the outside air will really add enough cooling to make it comfortable.
1) As previously mentioned, you need to keep the heater core cool, as the fan runs even when off (unless you or a previous owner modified it not too -- if you want to do that, do a search and you should find a couple good threads). Make sure the hot water cutoff valve works, and you can even put a manual one in on the return. There's also a vendor who sells shielding for the firewall area.
2) Heat can also leak in, as previously mentioned through the trans tunnel, or the windshield cowl area. Make sure all the seals are there, both in the trans tunnel and the ones that seal the engine compartment. Also, make sure the "fresh air doors" (can't remember the technical term) work and seal properly. It's possible for debris to get in and block them open. Ditto on the comment about the ducting having leaks.
Addressing those two areas usually resolve hot feet.
Mike