1. Will the washers you are using place even pressure on all sides of the raceways?
2. How are you determining you won't destroy the bearings with excessive preload force? It isn't clear to me from your comments or drawing to me yet?
3. What type of Bellevile washers are you using?
4. Have you considered wave type Bellevile washers since they place even pressure when compressed in all directions? Although they limit surface contact area they might be worth considering.
Would be very interested to know how you make out with this idea.