I think it is possible. Try this: Go to an intermediate frame and change the U value in the channel box (motionPath input node)... I'm just reading this out of a book, so hopefully it works.
Okay, when I try it, it needs something slightly different, Ctrl MMB drag to change the U value, and then key selected. Maybe.
Last edited by stwert; 05-03-2011 at 02:04 AM.