I remember an interview with him where he said he used to dip his fingers into a jar of Vaseline in the studio to help with his technique.
Good piece on Tommy that includes the Vaseline reference, "Mike Leech said that Tommy also kept a jar of Vaseline on hand, and he would stick his right fingers into it to help facilitate his technique."
"Like James Jamerson, Tommy Cogbill was a take-charge guy in the studio": Inside the recording of Son of a Preacher Man