I'm afraid that is just not possible and still achieve the design aim which is to have the same source code run with each library.
Anyway as I have tried to point out to you before GPSDriver is not just for HTC devices but should work on any WM5.0 or later device with internal or external GPS. A limitation I have seen on my HTC Diamond is that only the internal GPS can be used as its "External GPS" settings always seem to revert to the internal GPS even if you specify a COM port for an external one. My iPAQ 214, which does not have an internal GPS works fine with GPSDriver and an external Bluetooth GPS. I would have thought you would only need a separate version for devices running WM2003.