Interesting approach and i haven't seen Avocet's name in quite a while except I use their O2 saddles on everything I own. AFAIK, Avocet components were relabeled Ofmega stuff and i'm surprised the tapers aren't standard ISO.

Give your bearing idea a try and see if the spacing comes out adequately. The 1/8" bearing ball won't match the cup or spindle race curvature but may find their own bearing circle and work ok. Could you subastitute a Shimano or Sun Tour adjustable cup for the OEM one to get more thread engagement with the proper size bearing balls?