How can I create a one time mouseover that expands the stage

i have 4 circles on a stage that is 1000 px wide and 200 px high.  When I hover over one of the circles I want the stage to expand to 1000 px wide and 500 px high.  But I want that to only occurs once when I hover over any one of the circles.

SO I guess my question is how do a make a mouseover that only occurs once and does not repeat itself when I hover over that object again. 

Thanks!