as already stated, diesel has a very low octane value. somthing around 30-40 iirc, if the tank isnt going to be drained, avoid any sort of load while runing and use the throttle as spraingly as possible. avoid boost _AT_ALL_COSTS.
diesel will make the engine run lean, so the computer will correct this by adding extra fuel to richen it back up to scoich. computers have this ability built in because oxygenated gas a similar effect on the afr, although less of an effect than diesel.
just be real easy on that throttle, and fil with 93 or higher asap as already stated.
how did this person manage to get diesel in there in the first place? the diesel nozzle shouldnt even fit? are they sure they filled with diesel? you should be able to tell by the nice diesel exhaust smell.
does this car have a knock sensor, that should help a bunch.