To make it transparent just create a .txi file where to specify:
No't put any argument after "envmaptexture"
There are other options like making only black color to be transparent or to make tthe texture to light (sort of).
A short list of options available:
envmaptexture cm_baremetal / cm_Bright1 (first is shiny, second is fake self light)
# animate texture
# transparency on black
Just test few of them to see how it works (not sure I remember all that things).