Have been doing them on my knees all the while and managed to hit 30+ for max reps this way.
And I could do one rep unassisted.
How can I progress from one to 10 reps(or more)?
Do as many as you can on an ab wheel, then finish your sets using a stability ball. Add in ab wheel ISO holds.
Hooking up a band to it can either make a standing one easier or if you go the other way a kneeling one harder.
Does anyone else do them with loaded barbells?
You could also do multiple singles with the goal of reducing time inbetween singles to nothing so it's one continuous set. I had a friend who said it helped him with chin ups.