Surely they could be doing little things like converting to ethanol based fuels in the interim? As far as I am aware the current WRC Panta fuel isn't? But Panta do sell E85.

As for the car technology, perhaps some sort of KERS system? Given the amount of braking a WRC car does, that could have benefits? But I agree that it seems rather difficult to electrify a WRC car, given the distance and conditions they travel through.