[World Edit?] Invisible Floor?

[Etherealamd]

I had an idea to create a level floor high above the highest point in azeroth and basicly just have a character run along this floor using a macro to gain xp from exploration on wowscape. My question is how would I go about creating this floor with noggit? I know how to edit terrain, change terrain type, but I'm not sure how to make a whole new floor to walk on.. I know it's possible by looking at the video on the floor made to get to GM island.