Yes, it's a practical idea and I've done it.
The only problem you may encounter with sizing up on a mountain frame to match your road bike size is your top tube length. I built an all purpose commuter/tourer using a mtb frame which was at least 2 inches taller than my normal mtb sizing. Although the frame gave me sufficient standover clearance and also was able to get my bar height almost even with the saddle, my top tube was way too long but was able to compensate by using a very short reach 5cm stem.
Last edited by roadfix; 04-04-06 at 11:32 AM.