Yes, four wire is better. I've already grounded my one-wire sensor using a
radiator hose clamp and a length of wire for exactly the reason you mention.

But the question remains, what do you use for the 12 volt source? It would
have to be something switched on by the ignition key, duh, but what? The
coil?   Anybody know the connection point on later (3 or 4-wire) models?

I still say that if you could reprogram the ECU to cut down the open loop
time, or toggle it on or off, you'd save gas. Probably a lot. If you happen
to be going up a hill in the first minute or so of warm start, open loop
running, you're probably getting five miles per gallon. Leaning the mixture
might give you ten. Who knows.