[throwaway09223]

You can still do it.

rpath doesn't just apply to executable binaries, it applies to all shared objects including libraries. So, what you can do is modify the dyld that the python/ctypes module will eventually dlopen(). You should be able to find it by rooting around in the files installed by the module in question.

rpath is evaluated not just at binary execution, but also upon any dynamic linking -- including dlopen(). So it will work for both ctypes and CFFI.

Happy to provide further pointers if you need!