Shimano 11 speed freehub bodies typically don't fit older hubs.

8/9/10 freehub bodies probably would work on the older wheel, but probably would require a new axle and dishing the wheel. The old wheel uses a cassette and not a freewheel, right?

How much do you shift while riding on the trainer?

It should be possible to mount 10 out of 11 sprockets from an 11s cassette. Then, try to space the first 10 sprockets exactly the same as your other wheel (so adjustments would be a minimum).

Assuming you're not readjusting the derailleur stops, you would just have to be careful not to shift into the spokes.