Time to get off the couch and get on to the Bosu!
Yes, we do use the Bosu as a foot stoll.
The only isolated ab stuff I do is on a Bosu. This little half moon ball is KILLER on the abs and the absolute fastest way to target your mid section.
DISCLAIMER: Ab work is almost pointless unless you're lean enough to see your abs. You can't have a great stomach unless you can see it! I eat well and I run intervals 4-5x per week. That's the true secret to my stomach, the bosu helps give me a little extra.
Start with your arms crossed and have your biceps hug your head just behind your ears. I also interlock my fingers but if having your hands open is more comfortable that's ok too!
Lift up pressing your lower abs into the bosu. Exhale.
Repeat 3 Sets of 25. You will know you're doing this exercise right when your abs feel it after 4!