Yeah, it was one of the first things I've tried, didn't do the trick unfortunately... but thanks for trying to help anyway, it's appreciated.I have no idea if it will work on a car, but you can try this, it works for tracks.
[SHADER_REPLACEMENT_...]
ACTIVE=1
DESCRIPTION= ENABLE SINGLE SIDED
MATERIALS=
MESHES =
CULL_MODE= ON
I guess I'll have to try to edit the mesh manually in 3dsimED or something