The sarcastic beatings will continue until your moral improves.

As for the sand bag trick... Being a MN native, and drove a plow during college, the sand bag trick seemed to work best in cars/trucks that did not have a near 50/50 front/back weight distribution. I loaded my S10 with about 300 lbs of sand in the back and the fronts acted more like rudders through the snow vs. making any progress. Plus, it whipped sh!itties better, but it wasn't good for driving. I settled with one 50 lb tube of sand and accepted the 2WD's crappy performance. Then I bought a real truck.

On the XF, I don't know the weight distribution, but I bet it's close to 50/50. Put too much weight in the back and I bet snow and ice handling will suffer. 18" narrow snow tires I bet would be the best bet. Studded would be good if the state allows it.