I confirm that wakesurf is possible behind a Challenger (mine is a 180SP), ropeless.
I went ropeless this year with 1,000lbs of ballast (2 fat sacs) plus only 3 people on board (2 being under 130lbs). The wake is not great but surfing is still possible. I always sit one at one edge of the swim platform (this is also who I toss the rope to). FYI, I'm a 200lbs adult.
I put one fat sac on the ground and one on the rear seat, closest to the corner I want the wake to be.
I noticed that the trick to go ropeless is to remain close to the boat (~3ft) and work on your balance. You won't be travelling front and back on the wake like you would behind a Centurion though (elongated wake).
You don't need a Wake 210 or 230 with full ballast and 8 people on board in order to go ropeless.
This thing really gets addictive...