I'm pretty sure you can isolate the hams/glues if you think hard about them while pushing. I had this problem when I would squat, although I didn't realize I was doing anything wrong. I always assumed you pushed with your quads, but a personal trainer started helping me concentrate on the hams/glutes when I'd push up instead of my quads. Took a few workouts, but eventually I was pushing with hams/glutes and "secretly" working my quads all the same. Same goes with back extensions...instead of using low back to pull yourself up, use hams/glutes. Then again, this isn't the Shaun Recomposition Project, so perhaps Omega would be better to answer.