This is a tough exercise. Try it. I haven't.
Search for my push up blog post from years ago for the proper way to perform a push up. Hold a free weight in one hand. Use a weight that is doable and will give you a good workout for four sets of ten repetitions. When you are on the "up" part of the push up, twist your right side to the right in a controlled motion, using your right oblique, then return to starting position. Exhale when you go up, and inhale when you go down. Repeat for the left side. On repetition consists of twisting one time on each side.
My new fitness book Pocket Guide to Fitness edition II is out now!