People have used water injection to increase power for years
only when you needed more power. Might be easier to tune than alcohol injection. simple ones were manifold vacuum operated.

With some R&D you might be able to use a 5th fuel injector injecting into the air intake stream, and use a separate tank for the alky, with a low fuel alarm and instant ignition kill switch. Serious racers would keep the tank full all the time, or............................ once you knew how often you went through a tank of gas, you would make the alky tank bigger, so you run out of gas before you run out of alcohol.

There are different percentages of alcohol available at
...gasp! Walmart. -Bob