Windows 10: Run app 'full screen' in part of 4K screen

Hi All,
Sorry, I'm not quite sure where this question fits, but hopefully someone will find it.

I've recently upgraded to a 4K monitor instead of running 4 separate 1080p screens which is working very well except for the fact that I can't run 'full screen' without the app running on the whole monitor (obviously...). So my question is whether it is possible, either directly through Windows or a 3rd party app, to partition/frame the single screen into parts that will allow an app to run in full-screen mode within the frame?
Thx
Gav

Nothing???