Assuming he can afford a cheapo run about, that would be my choice. Fitting a DB9 with winter tyres may enable it to be driven fine but you can't do much about the rest of the Great British drivers.....
^+1. I just paid 395 for a 1.6 honda civic coupe with t&t to plod about in over winter. Handles the snow much better than our ep3 (nothing compared to a db9 lol), must be down to the 14" steelies and half the power but still a pleasure to drive