None of those ideas will make it any sweeter, it will just boost the gravity/ABV. Maybe boil up some maltodextrin and add it to increase mouthfeel, but that won't make it any sweeter? I suppose adding lactose would make it sweeter. But, if it were me, I would just leave it alone, but then again, I haven't tasted the beer.
You could make a tincture of the same ratio of spices in vodka and dose it to taste if you need an extra spice kick.