I don't think a rear wiper is too big of an issue. It may be an incovenience at times, but if its raining heavy enough that you can't see out of the rear, you probably shouldn't be driving in the first place.
Besides rear defroster, altering driving speed within safe limits is also a excellent option. The water slides right off with rain-x. Reminds me that I need a new coating in about 2 weeks.