I have played around with inverting from the floor but since I can't get my head and body backwards (since the floor is obviously in the way), I find that I don't get into the proper position. Because my hips are tight, I have a hard enough time getting my legs wrapped properly. With the ball, I can play around with my position, then let the ball roll out from under me so that I am holding my weight.
Anyway, I do admit that this can be dangerous since the ball can roll unexpectedly and dump you on your head, but I wedge it pretty well between myself and the pole. I position the ball slightly in front but to the side of the pole so that I can lean back and have room for my body. Photos are below. Be safe since the balls can be unstable, but realize there are ways to help you do moves you aren't quite ready to do yourself!
|From the floor, my legs aren't positioned in the right place|
|Using the ball, I have time to play with leg placement|
|Once I feel secure, I can let go|
|Then I can push the ball away and actually hold myself up|