Hi noskule,
i dont know if this helps but have a look here:
http://moi3d.com/forum/messages.php?webtag=MOI&msg=8965.3&highlight=yes

Hi Ben,

i don't know if your printer supports VRML (.wrl files), if so, i use this format all
the time via Blender, to have seperated objects with colors, or single objects
with assigned stile colors from MoI, on individual faces. I simply export as .obj
from MoI and in Blender i save as .wrl.

Regards
Stefan

OK, I figured out the way to do it is just export each part as separate stl file. Then import it into slicer software and mege them to an "objectgroup". The parts will then allign to each others original relativ position.
Thanks Ben