Not that easy, unless the URL pbfid thingy can be easily parsed into separate "post id" and "tracking id" parts — which I bet it cannot.

One alternative, which would require significant effort and investment but would be a brilliant way to outsmart Facebook's crap, would be to accumulate pbfids in a common pool such that, if a given pbfid points to post X, fetch a different random pbfid that points to post X. If the initial pbfid is not recognised, add it to the pool once the post is determined, either as a new alternative for a known post, or as a novel entry.

Of course, FB would hate it and would either try to expire old pbfids (and risk breaking "legitimate" links) or use legal threats, which would require them to openly admit that they don't give a shit about people's privacy preferences.