Step one -- put your twitchiest and strongest def lineman and line directly on the center low.
Step two - At snap of ball this defensive launches straight up to push the centers back into a vertical poisiton -- no attempt to penetrate just straight up
Step three -- Twitchiest LB or Safety who can lay the wood (ala David Fulcher, Mike Singletary, Ray Lewis, etc) have them launch launch as hard as possible directly midchest at the center to snap the upper spine backwards with the shoulder pads and not the helmet. (Legal hit)
Then when the QB gets pushed into the small of the back of the center he will crumple like an accordian.
You will likely give up the first down on the first play. A center will likely be legally injured every other tush push. Could do the same thing to guards.
The Eagles will need to dress at least 10 offensive lineman for every game and will not be able to run the play with non practice squad players by the fourth game.
The same could be said of the Bills who run this play a lot.