Most likely, it will be via a disc in the CD slot. I suspect they can compress the new Nav data and have the software uncompress it to the hard drive.
BTW, I sent and E-mail to Zenrin to tell them about a couple of navigation errors and they wrote back that they expect the first update to the EX35 to be available about August. I didn't ask them how it will be updated but I'll send a follow up now to ask that question.
BTW, Zenrin is the company that does the nav systems for all Infiniti models:'
http://www.zenrin.com
Mark