Given the size of the film compared to roll film (almost twice as tall and much shorter), even if you could extend the reel, I'd be concerned the film wouldn't stay seated in the spiral grooves. However, I think it's a wheel well worth reinventing. Maybe if there were a way to attach the sheets together end to end (with out too much fuss), it might help.

The alternatives for convenient daylight processing of sheet film are few and far between, not to mention usually way too expensive, so I think the community is well served by enterprising individuals coming up with new solutions (eg. taco method).