Unwrap Seperate By ID
Seperates UV Data based on Material IDs. This will horizontally move each seperate Material ID to its own 0-1 coordinate space.
Maxscript > Run Script > CraftTools_SeperateByIDvXXX
"Unwrap Seperate By ID" will then be found under "Craft Tools" in the
Customize Dialog. You can then add this to a Quad Menu, Hotkey, or
Toolbar from there.
This script should be run on one object
while the Unwrap Modifier is selected. It also requires that the base
object is a Editable Mesh or Editable Poly object.