get_python_lib supports an optional prefix argument:

    If 'prefix' is supplied, use it instead of sys.prefix or
    sys.exec_prefix -- i.e., ignore 'plat_specific'.

However the NT and OS2 platforms don't use the prefix argument when 
specified.

This problem was brought up a while ago here: http://mail.python.org/pipermail/distutils-sig/2002-November/003099.html

Andrew (the OS2 maintainer) claimed in the thread that fixing this would 
break OS2, but I don't see how. All callers of get_python_lib in the 
stdlib don't specify a prefix anyway. Anyone calling it with a prefix 
and expecting it not to be used is broken.