The main problem is that I don't have a mac to test anything.
I suppose the gl (platform independent) part could be done (easily?).
Look in the generator/glxx.py; this script has the platform specific code. There are #ifdef guards there for each platform.
Maybe run generator.py and copy-paste a specific snippet (from the generated glxx.h and glxx.cpp) and try to make it to compile on your machine by porting this code.
At lines 133-166 glxx::GetCurrentCtx() and glxx::GetProcAddress() are defined. These need to be ported. It should be straight-forward to port them.
Then you need to work your way up to the beginning sections of the script, adding #include and typedef statements where appropriate. This is going to be more tricky (I think).
The other thing is that for the platform specific part (iirc agl) there isn't any spec file to parse in the OpenGL registry. I think that this part will be very difficult to port.
If you are willing to code it, I will leave this issue open, otherwise I won't fix it for now.