There is no way to link in your own libusb any more. You have to use the statically included libusb.
Well, technically, it is not totally exact. To be more accurate, there is no more official way to link with your own libs. However, I did just that by hacking a couple of lines in the configure script.
Unless Con resort to cryptography and obfuscation, there willl always be a way :-)
If I weren't sucking with automake and autoconf script syntax, I would offer you new configure switches ie:
--with-libusb=path_to_pc_file Use system libusb libs
I have seen a couple of projects doing it like this. ie: Provide a safe version, let the flexibility to users willing to use their own version.
Firefox come to my mind.