Ed....This is exactly what they said. I actually went to Town Fair Tire, in Everett Mass. I'm not convinced that although we probably can do it, that we're guaranteed that the size different won't mess up the timing or something else. I did try to sell the BMW Blizzaks on Craigslist and Cars.com both by themselves and with the car, but no takers, and the season's just about over.
I think I'll just spend the extra money to get the right tires/rims for the Altima, and hope that Tax Refund Season will bring with it new and eager buyers for the BMW and the tires!
Thanks to everyone for your insightful comments!