OK !
<< Maybe your best bet is probably to convert it into a polygon mesh format and use a mesh offset function in a polygon mesh editing program.

Of course the funny thing is that is from a polygon program that this model is becoming! :)

http://moi3d.com/forum/index.php?webtag=MOI&msg=7250.5 and following!

It was for reuse it in Moi! :)

Maybe intersection - boolean diff of a box + 2 differents sizes of the surface ? :)