multisub vraydisplace channel

pa help po. my walls has 2 meterials. stone on exterior and plain white on interior. i've used multisub material. id-1 for exterior and id-2 for interior walls. i've added vraydisplacement mod for the stone material but the problem, it affects also the interior walls. how do i channel the displacement mod on exterior(id-1) walls only? any help will be greatly appreciated. TIA.

nevermind. i found a solution.
http://www.maxforums.org/threads/vray_displacement_multi_sub_objects/0001.aspx