Ab work out while putting a baby to sleep?!

Sometimes I amuse myself...I realized tonight that if i rock the baby forwards and back while in a sitting/leaning back position on the bed it actually gives me an ab work out. LOL  It sounds kind of crazy but if I do it right i rock solely using my core. I need to patent this "new mom" work out! And since my core is rediculously weak as i so lovingly dub it my "roo pouch", i'll do anything no matter how rediculous to get in a few "mommy crunches"!!