So I tried it. And it worked awesome. Booyah. 7400 Dura Ace 7-speed shifters (with "friction" 8th speed), M952 XTR rear der (standard cable routing), SRAM 8 speed cassette, KMC 10 speed chain. Shifts flawlessly in index mode through the 7 speeds. Can use the 8th "friction" speed to get to the 8th gear, although the friction doesn't seem to have much friction, so it kept slipping back down to the 7th gear over rough stuff.
Did Iron Cross with this setup, so hard core tested.