Arcording to: http://help.adobe.com/en_US/aftereffects/cs/using/WS3878526689cb916558 66c1103906c6dea-7e94a.html#WSB9C92251-D2B9-49de-8B7E-EE981AD17522 you should be able to seperate XY dimentions for 2D point controls.
But if i add a point expression control (or any other control that have a 2D position slider) the Separate Dimensions button is grey.
How do i split them?