Try a layered texture!
Just like the idea of placing a label on a beer bottle, for a variation on the ground surface, you could add a feathered alpha to your "variable" texture, and interactivly place it wherever you like.
Check the docs for "Layered Texture".
That's my quick and dirty idea
Israel "Izzy" Long
Motion and Title Design for Broadcast-Film-DS
izzylong.com