I am considering the possibility of bonding a supplemental seal to a bearings original seal.
One possibility would be to bond a trimmed-down commercially available seal to the existing seal.
Another possibility would be to bond a piece of sheet rubber to the existing seal, and machine a step on the flange which could be done on any good lathe in a few minutes.
Supplemental seals might be able to bond to original rubber seals using the same bonding agents that are used to glue O-rings together. Rubber original seals could be bonded to the outer race using a good rubber-metal bonding agent like E6000.
I have some rubber-to-rubber samples soaking in oil before I try to tear them apart. Bonding a supplemental seal to a metal original seal (Z or ZZ) would probably be the best, but a rubber-to-rubber seal would probably be the best bond.