I don't think it's possible. The gmt export options in the max plugins is where we define billboard and which side it rotates.
Maybe... I have tried it once, but whole object was rotating, not individual meshes, and it was rotating in very bad way. I am just making my first steps in rF2 modding. I use Travellers blender addon, but so far I only used it for exporting .fbx. But it is really meant to be for exporting .gmt, and I still haven't got to use it well in that way. I would preffer .fbx. Maybe then it would be possible to get something in combination with gjed. But it is complicated... Travellers script are also unfinished. Hopefully he'll find some time and motivation to continue them.
Hello guys. I tried a long time to create billboarding trees in blender but with no success but i have to say now i found the way how to do it. So the trees are rotate well with proper pivot point. When somebody would be interest i can share some instructions.
You can do it with Gjedit as well, as long as you find a way to assign 99% Alpha to Vertices color for GMT (can be done in 3dsimed, not sure if possible in blender), here is guide:
With 3dsimed, would it not be simpler to just isolate the texture and substitute with the desired image file of the same dimension? The object could then be resized at will?