I was wondering about this myself!
But, my situation is that 3 of us want to go to Beaches & Cream, just for dessert. We'll end up with 1 or 2 extra TS credits, I know, because we share when we're not hungry enough to eat a full meal ourselves, but we're not counting on sharing when we make our ADR's.
That said, we were thinking it would be fun to go to Beaches & Cream one night using 1 TS credit - drink water (1 of us could get a coffee, I guess) and then get a hot fudge sundae as our main course and a no way jose as our dessert, using just 1 TS credit! That way, we'd both use up any extra credits we may have, and avoid having to pay OOP for the dessert!
It's kinda wishful thinking, but sounds like a good plan, doesn't it?