There are three things to consider here:
1. Don't do it.
2. No really, don't do it.
3. For God's sake, don't do it.
Look, I know that most people on this forum are substantially better drivers than the average. Let me tell you a story about that...
TIA did a lot of testing last year at Nokian's Ivalo proving grounds for a video on winter tires, which is now available at
http://www.youtube.com/watch?v=enQIU3ywj6g. (Look at about 5:00 for the section on 2 winter tires vs. 4.)
I happened to be at Ivalo the same day TIA was there, so I happen to know that during filming, a highly experienced Nokian winter test driver with only two winter tires on his vehicle completely lost control of the car and high-centered it onto a snowbank so effectively that it had to be winched out. That's a guy who does this for a living.
You never hear someone say, “I'm a really good soldier, so I think I'll wear bright orange instead of camo and I'll just be very careful.”
Tests have continually shown that putting on only 2 snow tires is literally (and I use that in an actual literal sense) much worse than not having snow tires. If you want to save money by putting on only 2 snow tires, think about saving even more money by not putting snow tires on at all. You'll actually be better off.