Loading Unity package on the run

Is it possible to load in the webplayer a mesh contained in a unity package which is not part of the project?

I mean, i am a user, i upload a unity package on the server with a 3D model, and the webplayer places the model in the scene.

Or anyway, my client needs to upload on server new models of fornitures, from time to time.
I need to find a way to let him upload those models and make them droppable in the scene, so must be a type of file which unity can load in runtime, with textures and materials.

Fbx i read wont work if not licensing an external tool, which is not possibile since is a webapp and the load time will be critical.

What do you think would be the best solution?
Thanks.