To be fair it was Fox that didn't directly ask the question, though interviewer did thoroughly enquire about other pardons, Hunter Biden, Jan6 jailed, etc, which would have been a good opportunity for him to mention Ross.

Only thing we can do is make it worth his while to keep his word, which would be out of character for any politician, but especially Trump.

His ego is extremely sensitive; probably most effective way to put pressure on him is viral meme campaign making him look stupid if he doesn't follow through.