Can you do this? Have a part of your model act as a billboard (always faces the player)? I've looked around and the only documentation I've found has referred to Torque 3D. I've tried prefixing my mesh names with "BB::" and "BB_" with no success. I can't access the documentation for Blender's .dts exporter as all links seem to end up dead, and the only kind of support the exporter seems have anyway is for autobillboards, which I don't think is quite what I want, reading up on it.
I'm not sure how .dts exporting works in Milkshape but I think that the DTS Exporter Plus has support for it. If anyone can quickly test to see if that works and then get back to me that'd be great! Thanks.