I know that I can overload getLocalMachineIDs and I did create my own. Nevertheless I suggest to change the current implementation because it gives different results on the same physical computer. Not what you want in a challenge response unlock mechanism...
On Windows (at least on Windows 8), a 32 bit binary yields a different result than a 64 bit binary.
On OS X, an AU gives a different result in Garage Band (where the plugin is sandboxed) then everywhere else. Here, the discrepance lies in
(I haven't tried it, but on OS X the folder "~/Music/" should be accessible on sandboxed applications, according to http://www.juce.com/comment/302487#comment-302487)
The fallback mechanism that uses the MAC addresses gives equal local machine IDs in all cases, btw.