Can you upgrade the HDD in these things?!

I've looked around a bit on iFixit, but I don't really think there's a thread so far which really answers this question directly: is it possible to upgrade the hard drive in the 6G iPod Classic, PAST the 160GB mark?! I have a friend who has an enormous music library and he's wondering if he could get one and upgrade the hard drive.... The upgrade isn't really the problem, rather the problem is whether the iPod will recognize the HDD, and whether iTunes will recognize it?

Thank you all :)