I have a little experience with the running/carrying problem. My solution was to carry a J frame revolver in what is known down here as an ass-pocket holster in sweat pants that had a zippered right rear pocket. The ass-pocket holster is normally made of rough-side-out leather so it stays in your pocket when the gun is drawn, loosely boned to keep the cylinder upright and the grips just below the top of the sweat pants pocket. I can't think of any reason you couldn't do it with a P-64. or you could try the belly band holsters from different makers, I think mine was a Binachi and I had it cut a little to fit better. If you are a humid, warm climate you may want to consider body powder between you and the belly band Good Luck
hairypolack
I was @ smartcarry.com today and they claim that their holsters will not move even when in active situations, looks like a good means of deep concealment and it may work in your situation.
Hope U find a good holster
CKL