Plugin to use STL models as external mesh references. Check-out the example.
The plug-in to encode mesh models is not chosen by file ending but by media type. So make sure your STL models are delivered with media type
application/vnd.ms-pki.stl. In the response header of the STL file you should find:
<group ...> <mesh src="../path/to/model.stl"></mesh> </group>