Mon Sep 16, 2013 3:50 am by Alge
You can already do this.
You need to make a Mapped Key with 2 Steps. Step 1 has a Video FX Action (Create) that recreates the Viewer but at the larger size. Make sure to include this Mapped Key in the Hold Mapped Key option again. For best results set this Step to not advance for at least 0.1 seconds and to only trigger once. Step 2 has another Video FX Action (Create) that resets the Viewer back to how it was. The Target of both those Actions must be a particular Slot.
Set this Mapped Key to execute a Step when pressed or released and then also set it as the "Hold Mapped Key ..." option for the Video FX Viewer where you initially create it.