When debugging you should do a recursive print of your MPMoviePlayerController's view, that'll show you the entire subview hierarchy of that view. Like so:
po [[[self player] view] recursiveDescription]
Look for the MPVideoContainerView which has 4 subviews. The should insert your subview between 2 and 3, the MPVideoView which draws the video and the MPInlineVideoOverlay which holds all controls.