Select the whole void, copy and paste it into a new project as a layer.
Give that new project/image file a transparent background (checkered look).
Now set the layer which holds the void from Normal to Blending option Multiply.
Now you can put any layer with camouflage behind it.
Play with those blending options, so you know which does what. Ik might give you other ideas as well
http://www.simmerspaintshop.com/foru...p-608/?garpg=2