We sometimes suspend a band and perform standing crunches. Just hold the band in front of your forehead and bend over and contract as hard as you can. We also do this on the lat pulldown machine.
Standing crnches are good and i do one to the sides like that called lumberjacks.( idonno) they hit the obliques good to. i Have tried straping them to the bottom of a decline bench but havn't found the right ancor point yet.
Let me know how it goes...I really like those. You can also angle up for oblique crunches,a nd hold the bands higher to hit the upper portion of the ab wall harder.