One way to solve this is by editing the __init__.py module of the package containing the C extension and tweaking the __path__ global so that the correct shared modules for the importing platform is found. I've never tried this, but it should work...
Note that the idea of packages tweaking their __path__ is not very future-proof; one of the things under consideration elsewhere as a distribution mechanism is to place a group of modules in a zip archive (either the standard Python library, a package, or perhaps the library plus a set of packages needed by an application).
I think it's worth looking again into the issue of where package-specific shared libs should come from when the package itself is loaded from an archive.
--Guido van Rossum (home page: http://www.python.org/%7Eguido/)