Ah, I had misread the original request that you were looking to make the workspace smaller.
As far as I know this isn't supported. I did some quick CSS hacks to essentially achieve the same result but, predictably, they cause coordinate shifting, over-rendering for blocks dragged outside the workspace, and scrollbar issues. This might be something that's possible to solve with a plugin but it would be fairly involved. I would be curious if anyone else in the community has done something like this before and how they managed to solve it.
Regards,
Ben