Roll Out Animation

Hi there,
I have a number of simple vectors (to form the main background) in the stage, and was wondering how I could allow each individual vector to animate after the cursor has rolled off it. My intention is to have an alpha fade in, i.e 100% when the cursor is off the vector, down to say 40% when the cursor has rolled in and is hovering on the vector, and then fade in from 40% to 100% after the cursor has left the vector over the course of a few frames. I’m sure this is possible, but I have yet to work out how exactly.

Any help would be greatly appreciated.