Then you should have no worries mixing tires front to back. In fact, I've been running two different brands of snow tires now for 3 winters. Never a problem.
If you don't think you will get much snow, might I recommend checking to see if you can get a set of Goodyear Aquatread tires. I have seen these used for winter (snow) duty on FWD cars here in Calgary. They seem to work well so I would imagine that they would be adequate for RWD. The only thing is that they may not be available in the proper size of 245/45's for the rear. However, for winter duty, you will do just fine with 225/50's, though I'm still not certain they are available in this size. Pick up any car mag now and you will see listings for snow and "off (all) season" tires. They'll have all the available sizes printed.
A pair of Blizzak LM-22's will serve you well. They are quite good in dry road handling and will get you by in fairly deep snow. Rain should be no problem. You do NOT want to use these in summer, though.

One last warning: YOU CANNOT DRIVE IN A SPIRITED FASHION WHEN YOUR TIRES ARE MIXED LIKE THIS!