You could add a giant snippet on your page and design everything in there. Snippets do not have layout so you have the whole screen available for your content.
If a layout defines multiple placeholders, pages based on that layout have multiple places to put content. So the form editor would need a way to zoom into one of those "holes" to make it work without the snippet workaround. We talked about this when we were building layouts but it never got high enough on the backlog, unfortunately.
The only suggestion I have is to temporarily change the layout to PopUp while making your changes, then change back to the correct layout after having adjusted your content.