How about a work stand that holds the frame by the bottom bracket shell?

Nah. Have to have the BB out.

I kind of like the "inside the seat tube" idea. Any "production" stands use this method?

Come to think of it, an adapter wouldn't be too hard to make. The expander/wedge idea, but made separately, as a separate unit. Insert into the seat tube, secure, leaving 5 or 6 inches of the fixture exposed above the seat lug, then clamp the fixture in your standard clamp work stand.
Think that would work?