@ lyinawake

If I understand you correctly, this requires an advanced setting of multiple shortcut keys.
First, you need to make sure your Fullsreen display is set to Preview.
Secondly, you need to set up a shortcut key for FullscreenOn and set the input to Preview (doesn't really matter what you select as an input).
Thirdly, you need to set up a shortcut key to send your desired input to preview.
In the Advanced Tab of that last Shortcut Key, you need to trigger the key you selected in the second step, thereby, every time you press the key from step 3 it will display as Fullscreen.
If you want to turn off the Fullscreen, you will need to set up another key for FullscreenOff.
You can do the same for multiple different inputs if you so desire.

Hope that helps.


Ice