I've done this when I have written some OO Perl (in 5.8) to be able to use the same functions across different platforms but with different parameters (such as Windows and Unix naming conventions). In that case we did it pretty much in the same way as any other OO library, where the parent might define a function as empty or die if its not in the child so we could make sure that the proper libraries were being loaded and used.

Depends on what you are doing, and how.