if you move at half the frame rate, that is the same as moving every other frame. That gives you a steppy motion. If you could move at half a pixel per frame, it would work.
So I don't think this is the right answer, unless I misunderstood you.
You can set x and y to non-integers, but you will likely see distortion as it tries to render on half-pixels. Most folks will not see single pixel movement as steppy.
Flex SDK Developer
Adobe Systems Inc.