i know exactly what you mean -
unforuntately DesktopCoral cannot do this.
the desktop area not used by DesktopCoral will behave like your normal desktop, ie you can expand stuff inside it.
but within DesktopCoral region, if you moved an app there and maximized it, it would jump out of the coral and into the main desktop region.
it's probably possible to do what you want by writing using some low-level virtual monitor driver, which would be a very fun idea, but outside of scope of this small project for me.
may i suggest you look into buying a dual monitor setup for your computer. I use one and it does exactly what you are describing, but with two desktops side by side, one on each monitor, and i could never go back to a single monitor. it truely is the only way to live.