Would it be taboo to mix Diet Coke and something like makers? Going to cut back on the beers this season
Have you tried to drink Maker's Mark neat, though? A cube of ice will tone it down a bit, if necessary. Also, if you like a sweeter wheated bourbon (like Maker's), give Larceny a try.
I'll throw out another low-cal option: Crown Royal Peach in unsweet tea. Surprisingly good.