Press the bar overhead from your upper chest, but instead of locking your arms out, lower it behind your head to about ear height, then press it back up and forward to your upper chest again -- front, back, front, back, without ever fully straightening your arms. Keep the bar low, just skimming the top of your head, and keep your elbows in front of your body rather than flaring out as it passes overhead. Because your shoulders never get a break at lockout, this stays under constant tension in a way a normal press doesn't. Use a fairly narrow grip and go light -- control matters more than load here.