More details about the pond (size, existing fish population, etc.) would help, but adding threadfins in the spring would definitely help them establish if they can get a few spawns in before the bass start feeding on them.

A 3-4" bass should not be able to swallow a 3-4" threadfin, but after that it is only a matter of time. Based on everything I've read and from my own limited experience, threadfins are a great addition in the south. In Oklahoma, they'll die off about 1 in 5 winters, IIRC from Bob's book "Raising Trophy Bass." I think 45 degrees +- is their limit.

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