How do we change / remove ical and address book skins...

Is there a way to out-right remove the 'Leather' skins that Apple has used with iCal and Address book. We had a client jokingly ask us if we were working on kids computers the other day. Not impressed to say the least.

We've read about the hacks floating around in the internet wilds but would prefer a Mac-enabled way of changing this. Why isn't this an option in the app preferences?