I can't remember too many details, I probably have notes at home, but a couple years ago I tried something somewhat similar. I steeped specialty grains only, did a boil for hopping purposes, cooled and transferred to a small keg with spirits and carbed. I believe I did an IPA with whiskey and a stout with dark rum.
They really were not close enough to beer to do the trick for me. They actually did taste ok, just more like bitter seltzer than beer. I remember the IPA tasted like a whiskey and soda with bitters. If I had the time and inclination to tweak the recipes it seemed possible to make a decent beer substitution with very few carbs but regular amounts of alcohol.
I was much happier with my ultra loe carb beers that were just regular procedures but very low OG and enzymes.