Alcohol injection is more commonly used in NA applications because it doesn't require the higher pressure like water does to atomize properly. Water puts the fire out on NA setups. Alcohol adds fuel, and that's not all bad, but I'd say it isn't necessary on a boosted setup if you're just trying to extend your knock ceiling. If you want another fuel source, look into propane injection.

Some people mix alcohol into their water injection systems. It keeps it from freezing up in the winter, and since ambient temps are lower, your engine is already cooler. If you're not close to the knock ceiling, (keeping exhaust temps well under 850°C), then you'll be able to make a few more horsepower by adding alcohol. But the inert gas which is water vapor actually does just fine at increasing your compression while lowering combustion chamber temps.

Using alcohol is one of those things that just takes some expiramenting. The water injection setup doesn't have to be modified at all to use it, so... I'm sure you'd find a way.