IFI... please don`T do that!
Conditions at the engine nacelle, are way diferent than those at the wing leading edge, wipers and ice detector! Due to engine suction, the pressure and temperatures are lower. We would have to do some calculations or measure it for real, so lets just guess some numers. For instance if you have a TAT 9ºc, at the engine nacelle you might have, lets say, -5ºC.
Remember... if it is written in the manual... it`s true! more it`s sacred!
Fly safe
cheers