in practice, it's not so hard. it looks just like respecting their identity, which they think is fallacious and worthy of ridicule, and that will usually be enough for them to crack after some time
fascists will be fascists, and they'll think being kind and respectful to a troll is funny, but there's not much else one can do about it. they were going to laugh anyways, so you may as well make the best of it
and sometimes, rarely, it can be what leads someone out of that mindset