Rear foglight button to turn on/off angel eyes? You're a bit late.. Razcal has the switch and has already started doing the exact same thing.
Yes, it's possible to do.
You'll need the switch, harness, automotive relay, and a bit of wiring know-how to do this.
My angels are hooked up to a relay, I wired them up differently. I have other switches mounted in my car to do other things.. (fold the mirrors, start engine button, brake light kill switch, etc.)
Nascar - depends on the year of your car, it could be as simple as swapping out your daytime running lights module, or it could be a little more complex as wiring up a separate headlight switch.