Camera per pixel mapping

[enigma]

Hi,

 

How do you apply alpha channels in camera per pixel mapping?

 

For example,I have a speedtree model in the scene (speedtree has alpha's on its leaves, right?) when i render the scene with camera per pixel mapping somehow the areas in which the alpha's on the speedtree should be transaparent, becomes annoyingly obvious.

 

Is there any workaround on this one? Is there a way to carry the alpha on speedtree when you render with per pixel camera map? Any links or tutorials on this matter would be very helpful.