Even if I weren't allergic to malt & malt bev's I'd just go for adding vodka or rum to my soda. The reason being is that I'd want to make sure that the resulting malt bev, which is further sweetened, doesn't start fermenting again. This requires additional preservatives, or pasturizing, neither of which I'd prefer doing if I don't have to.
It could stay just fine and not ferment in the cold temperature though. Again though, I'm allergic so I'm not going to try it out, but sounds like it'd be worth at least trying if it wasn't for that.
Secondary: GF Czech Lager
Waiting to be kegged, Italian Primitivo
Kegged&Ready: GF Orange&Coriander, GF Honey Lager, GF chocolate ale, GF English ale, Island mist (zinfandel), Island mist (cbry malbec).
Bottled: Infected Mead, Dry Hard ciders, Accidental Sorghumwine, various unnamed.