More on the unit designer as battlemech garage: It shouldn't be too difficult to break each mesh into component parts that can be interchanged as armor, so you could have a basic mech with possible upgrades like a radar or communications dish on the shoulder, jump jets, missile launcher, and so on. The equipment categories would have to be renamed.
I'm seeing brushed metal, cyberpunk, style windows with loose wires hanging out, category names as green LCD displays.
EDIT: Some models.
http://sketchup.google.com/3dwarehouse/search?q=battletech&styp=m&btnG=Search
http://sketchup.google.com/3dwarehouse/search?q=mecha&styp=m&btnG=Search&reps=1
http://sketchup.google.com/3dwarehouse/search?q=gundam&styp=m&btnG=Search&reps=2
http://sketchup.google.com/3dwarehouse/search?q=transformer&styp=m&btnG=Search&reps=3
Any kind of giant robot would do, I think. Just retexture them and make enough minor changes that they won't be immediately recognizable. If you can find the whole catalog of Battletech mechs, that would be great because you could use their stats and equipment; but I don't think it's necessary.
Also, you might have to change the meshes to make them fit the Elemental skeletons and animations. At least until someone figures out how to make our own skeletons and animations. Even then, Battletech body types are quite different and may require a dozen or more unique skeletons. I'd look into all the available skeletons and animations to find some that might work for mecha and focus on those first.