Austin Homebrew Supllies offers an option on all it's kits:
1% Alcohol Boost:
Add 1% alcohol to your beer without compromising its flavor. Brewvint Alcohol Boost is 55% maltose/45% glucose, a very fermentable mix with little flavor contribution.
I'm curious about anyone's experiences with this. Does it really not affect flavor? Could I (theoretically) add several of these? Any other drawbacks to them?