many craft that used an injection or additive had far more than one use of that substance onboard. The heat was the major issue. For example, Bf109s and Fw190s with MW50 injection onboard carried 30-35 MINUTES of the liquid. Some US planes with water injection also had 30 MINUTES onboard. When you look at AH flight times and 2x fuel burn and people taking 25% on higher-capacity-planes, most aircraft would run out of gas before they ever run out of WEP. That's not counting those that simply injected more gas into the cylinders, or those that just upped the compression and RPMs in the engine without needing an additional additive.
It's really a non-issue.