Potters "Wand Magic" positions roam and aren't assigned to particular spells from what I understand. They just happen to be at the more popular and difficult spells to help people.
So remove the difficult spells and you don't have the helpers - and maybe even reduce the lines since it'll work.
And why not get multiple rides at once like FP? You just get paged to return at various times. The computer can figure the logistics out.
The issue I see is groups. What if you get paged to return but your other half is waiting longer because of a gap in the time it took you to tap and register or a sudden jump in returns?