I found by accident a paper today, where tomatoes leaves were inoculated with Methylobacterium. This interferes with ethylene production in the leave and heightens resistance against Ralstonia. So your idea about transferring healthy phyllosphere seems also to be a possibility to jumpstart the system.

“Ethylene emission and PR protein synthesis in ACC deaminase producing

Methylobacterium spp. inoculated tomato plants (Lycopersicon esculentum Mill.)

challenged with Ralstonia solanacearum under greenhouse conditions”