I have no idea why you would recommend NOT using a brown sugar substitute for this dish. I substituted almond flour for the whole-wheat, and 1/2 cup Sukrin Gold for the brown sugar. It turned out lovely and delicious and a great dessert without my body going through inflammation and a jump in my blood glucose.
I used 1/2 cup of the sugar free blueberry jelly (that stuff is yucky, but I have to have some sweetness) and added some smashed raspberries and blackberries. My picky husband even liked his with some ice cream. Delish!