select line by mouse motion

I'm trying to catch the lines the user selected by the mouse MOTION (i.e. NOT by clicking) WindowButtonMotionFcn and WindowButtonUpFcn are defined only on the figure that mean I can have only the "current point" value (but not current object for example..) and thats doesn't help me for identify the line the user have selected.
anyone can help me???

thanks
dalhad@gmail.com