ECW realtime update

Hi,

I am trying to implement a sort of "loupe" tool as part of an AE plugin. It's actually a tool that helps position a 2d point/pin in the comp. So far, when I move a 2d point i am able to draw the portion of the comp around that point in the ECW (via an ARB param). The only issue, I must release the mouse button to see an update of my ARB viewr in the ECW. 

Is there a way to continuously update the ECW drawing (or at least that ARB param) while draging a 2d point ? thx.