One would be to use it to assist in lower ab moves like leg walks. Just put the band around your foot and hold the ends in your hand. Use it to help control the movement as you life and lower your legs.
Here's the movement (
a and
b), just use the band around your feet and into your hands. And for all of these, you don't need the bench!
You could also do leg pulls in. Sit in a V with the band around your feet and use it to help you stay up while adding resistance.
Here's
a and
b for this one.
For the obliques, you could do standing side bends with the band under your foot and in your hand on the opposite side that your working.
You'd be doing the same movement (
a and
b) but with the ends of the band where the dumbbell is and looped around you foot.
Or put it through a banister or something else sturdy and do spinal rotations.
Here
a and
b.
Other ideas would be to simply do a weighted sit up by looping the band around something behind you as you lay on the floor with the ends in your hands (making sure there's tension) and doing the sit up. You could also do a
woodchopper which is similar to the rotation but has an up and down motion. Hope the pictures help!