If you want your pushups to be all chest and little legs, simply destabilize your feet on a wobbly surface like kettlebells. The brain will feel the lack of stability in the feet and force the chest and shoulders to do all the work. It also makes the core work extra hard in keeping as mush weight forward as possible, making the chest cry for help.
You will see the feet and legs begin to stress laterally by the third rep.
https://youtu.be/dhOom5YbzIU
