My duaghter has been doing the exact same thing since she was about 6 months old, no matter what I give her to look at, she's over it within seconds, and is a vertual houdini when it comes to wriggling around under the stupid strap thing on the changing table.
When I hold her feet, she just raises her bum up off the table, and twists- i'll still be holding her ankles, but i'll be getting the rear view.
I once heard a tip where you hold a balloon in your mouth and blow it up and then let it down and stuff to keep the babies attension- I did try it, but found I needed a hand to hold the balloon while I inflated t, and maeve just wanted to grab a hold of it and play with it herself- which I did let her do, figuring, hey, whatever keeps you still- but she realised within 5 seconds she couldn't blow it up, and was extra annoyed.
Maybe baloon in conjunction with belt, and some speedy wiping!!!
Plus- get used to it, maeve is now almost 13 months, and still fighting every change.