It's possible to do by using a disc /drum master cylinder and switching the lines. Basically the reverse of what is normal. I agree with everyone here, it's dangerous and I would not waste the time or effort to make it work. A majority of your stopping ability comes from the front brakes. Why would you want drum on the front and disc on the rear? Not a good option.
I would wait and do it right... There is one thing I don't go cheapo on and that is brakes. I like to make sure I get home in one piece. And with that, I hope everyone has a safe holiday season.