Rather than changing the unity codebase, you might consider using desktops to arrive at your desired result.
Example using Compiz Desktop Cube in CompizConfigSettingsManager
Open CompizConfigSettingsManager (
ccsm) and change settings to match the following:
Open terminal 1
Use the keyboard shortcut CTRL-ALT--> (right arrow) to go to the next desktop to the right.
Open terminal 2
Use the keyboard shortcut CTRL-ALT--> (right arrow) to go to the next desktop to the right again.
Open terminal 3
Use the keyboard shortcut CTRL-ALT-<- (left arrow) to go to the previous desktop containing terminal 2 (or twice to get back to terminal 1)
Use the Viewport manager in CompizConfig SettingManager and assign a key combination to go directly to the desktop of your choices