I am sorry if I revive an old topic, but I was looking for the same and I think, it can be done now with heating films.
For example like this:
http://www.aliexpress.com/item/V3-si...434694866.html
I didn't find the best solution yet, because the available items are mostly for newer cars, but I think, it's possible.
There is a company, which seems to make customized films too, but I didn't contact them yet:
http://www.heaterfilm.com/html_l.aspx?id=1389
---
And for the guy, who screamed BLOWDRYER the whole time: I had heated mirrors on my old Rover 620si and you can not compare a heated mirror with a blowdrier. If you want to use a blowdryer, well, your choice, but there are people, who actually like to have it the easier way and if they can afford it, why not? Not everybody is so unsophisticated, like you