Personally for me, the results which are gained from such practice over time are far greater than the need to force myself to keep up playing. But if you feel like you need a greater motivation to play these exercises, here is what works absolutely wonderfully for me.
Instead of playing every exercise from Part I and most of exercises from Part II in C major, like it is written, I play them in different modes but use the same fingering. You too, can choose any mode that you want and play each exercise in a different mode.
In fact, you can create an entire system of modes (Lydian, Ionian, Mixolydian, Dorian, Aeolian, Frygian, Locrian, Pentatonic, Blues, Octatonic, Whole-tone etc.)
You can even go wild and play 7 modes of limited transposition as used by Olivier Messiaen.
If you don't know the names of these modes, no problem - just play everything from C but with different accidentals (1 sharp, 1 flat, 2 sharps, 2 flats, 3 sharps, 3 flats etc.). This will keep your mind engaged and focused.
Try this approach in your organ practice today. I have to say that playing Hanon exercises in such a manner is not at all boring. In fact, it is very musically interesting and even addictive because in addition to supercharging your organ technique, it also helps to improve your music theory skills.
Moreover, because the modes constitute an integral part of modal improvisation in the 20th century French style, playing Hanon exercises using different modes will definitely improve your improvisational skills.
By the way, do you want to learn my special powerful techniques which help me to master any piece of organ music up to 10 times faster? If so, download my video Organ Practice Guide.