A really good question, brightspark, and I'll add it to the 'wish list'. I'm sorry to report, though, that at present there is not a way to do it.
While it seems pretty simple idea on the face of it, it is actually a 'non-trivial problem' as a designer friend used to say. Just one tiny example of the nuances - which as an AdWords support person, comes to mind right away:
Imagine thousands of emails from thousands of advertisers in 24 different time zones, asking questions related to their statistics - which appear to me in PST, and to them in an entirely different way...It just makes my hair stand on end!
OK, I'm better now.
But seriously, it's a great idea, and one that is already being tossed around. So I'll add your vote to the list. ;)