What kind of end result are you seeking?
Adding sugar will encourage yeast to grow, which may be what you want if you are seeking carbonated or alcoholic drink. There may also be a lot of natural sugars in the sprouted grain already.
You could malt the sprouts and use them in ferments like beer, small beer,
sourdough.
Wild fermentation by Katz is a great read for this kind of fermentation experiment. I think
Sally Fallon has some sprouted grain ferments in her book Nourishing Traditions. Most of Fallon's recipes use whey (live, as in from a fermented source like labneh, not from cooked cheese making) as a starter.