You might be interested in Automatic Sync Technologies’ CaptionSync automated web-based captioning service (https://www.automaticsync.com/caption/broadcaption.htm). There is no software to buy, it’s just a use-it-when-you-need-it service. You can choose to get back Digital NLE Captions — a black MOV file with the captions at the top. You place this on your FCP timeline and it is embedded in the VBI when you print-to-tape. No shipping tapes, no gen loss, no FedEx, and not very expensive.