Originally Posted by FastJake

Cable pull is slightly different, but I've used a 7 speed downtube shifter with an 8 speed cassette. It worked fine for me. The last shift isn't a "click" but rather it goes into the friction portion of the lever travel. That doesn't matter though since it's only 1 shift and is limited by the limit screw. It was actually the smoothest shift in the whole system.

But to make any of this workable you must specify: what rear derailer? Dura Ace or something else?