Will a molly bolt expand or just shatter when it's thirty below zero?

Some idiot tried to steal my mail today and in doing so accidentally ripped the mailbox off my house and broke it into about 40 pieces. Some parts are ruined beyond repair, so I'll have to go out and get a new mailbox.

I know that attaching the mailbox will mean I'll have to drill holes in my stucco with a masonry bit (the old holes were destroyed when idiot ripped it off the wall), then put in two molly bolts, then screw in the screws, then hang the mailbox on the screws.

Problem: it's the dead of winter. It's -28 right now not including wind chill. I won't get my mail without a mailbox. But won't the tines of the molly bolts just shatter when I screw the screws into them? Is there something I can do to stop this from happening? Or should I use another form of attachment?

I can't afford to be going back and forth to the hardware store: it's a 20-minute and $2.30 bus ride away. So it would be a big help to know whether I should be using something else to attach it.

(Incidentally, I live in Canada; in my neighbourhood, having a mailbox on a post (like in the US) is actually against regulations and I would not receive mail. The mailbox has to be attached to my house. I don't even have a post.)

Thanks!