Playing Movie Clip Backwards

I know that this has been the topic of much discussion, and I have searched (unsuccessfully) this forum, Macromedia’s, and the one a Google. So here goes:

I have a movie clip loaded into another. In this clip, I have different images, each motion-tweened into position every 11 frames. There is a stop on each 11th frame, therefore I can easily control the forward motion of the movie with a “forward” button in the parent movie.

However, I am having difficulty making a backward button that will stop on every 11th frame. I have used the following code successfully, but it just plays all the way back to frame 1, then stops.

myButton.onRelease = function() {
_root.myClip.onEnterFrame = function() {
this.prevFrame();
};

How do I tell it to stop on every 11th frame?

Thanks in advance.