Hi
Sorry, that is not possible with a single grid graph.
What you can do is to create multiple grid graphs and then use the graphMask parameter on the seeker.StartPath call to specify what graph you want a particular unit to use (you will have to modify the AIPath script or whatever movement script you use to add that parameter).
See http://arongranberg.com/astar/docs/class_seeker.php#ab50a876ab529ceb3eb9b97deb5a48d1e