I think that's your best bet. Under no circumstances would I recommend grinding or otherwise taking any real metal off the caliper bracket. That's the anchor to your ability to stop, though since it was the rear brakes it wouldn't have been as bad as doing it to the front set.

Start saving up for a good, quality set of slotted rotors if you'd like, from a reputable source. They're not that expensive, and you'll be better off than with an iffy set of drilled ones.