Looks compimiclatedAlthough its for an SSD, have a look at this:
http://www.audizine.com/forum/showthread.php/650767-DIY-Upgrade-MMI-3G-HDD-to-SSD
I personally wouldn't do it either. Too easy to break something both hardware and software and the 5F units are lots of £££ even from fleabay.
Easier just to chuck 2x SD cards in the front for an extra 64GB of space. Lot less time and money involved. From what I read the SSD isn't that much quicker compared to the original HDD.