Ronne and Amy,
If you could tell us what it is about the roll outs and oblique crunches with the band, on the ball, that you don't like we might be able to help more.
The best general advice that I can offer for the roll outs is to make sure that you don't go out too far if you are feeling discomfort in your lower back. Also, really concentrate on pushing into the ball with your elbows and contracting your abs when you pull back in. The last piece of advice would be hand positioning, play around with it a little bit to see if one of these suits you better. Hands further back on the ball, more forward on the ball, hands clasped in a double fist, hands just placed together in a prayer position, or hands separated a few inches and placed parallel to each other.
For the oblique work, play around with the positioning of your legs, try a towel instead of the band, or eliminate it altogether and just extend your arms out past your head, or only hold your hands by your head and work up to a full extension, try positioning your hip higher or lower on the ball, and finally, make sure your mat is very "sticky" so that your foot and the ball don't slide.
Again, the details you give us, the better we can help you, but I hope these suggestions might get you started
Good luck,
Mattea