Development of Creative Commons licenses

[Neil Stockbridge <cc AT dist.ro>]

If I have a 3D model that I license using BY-SA, what is the meaning of
"derivative work"?  What I would like is for the licensee to be free:

 * to incorporate the unaltered .blend file with their software product
and be able to license the software as they wish (even with a
proprietary license)

..and for the licensee to be obliged:

 * to provide attribution
 * to release any improvements or fixes to the model under the BY-SA
license before distribution with their software (whereupon they are
distrubuting an unaltered .blend file as above)

Is this already covered by the BY-SA license or is the composition of
the .blend file with the software object code considered a "derived
work" and therefore subject to the BY-SA license?

I'm looking for a sort-of LGPL for meshes.

- neil