You can do what you said, but I don't think you're going to get what you think... A drink that tastes like a low OG drink but kicks butt? It can be done, but not quite that easily. Just step feeding a regular beer with simple sugar is going to give you something really dry and you will certainly be able to taste the amount of alcohol, it isn't just magically hidden because you fed the yeast later. Maybe with a good enough recipe design, extended aging, etc. you could get what you're looking for, just do some more research.