One classic approach is to “hang a lampshade on it.” If he really shouldn’t have survived that, you can have a character in the story point out how lucky he is. It calls attention to the fact that the plot is implausible (although this is could be a clue that there’s really more going on). But at minimum, it tells the reader you’re aware of it.
John Bois’ online story “17776, or What Football Will Look Like In The Future” goes a step further. Someone who’s survived in a way that wouldn’t be possible in the real world suddenly breaks character in the middle of a conversation:. The author makes a joke out if it, but still has his mouthpiece say that he’s breaking the Fourth Wall for the sake of your personal safety and well-being. “I can only do that because I am unkillable. [... Y]ou are extraordinarily killable. [... Y]ou'll be remembered as the person who died in some crappy cave because you read it in a story you read online about sentient 178th-century space probes who watch football all day, even though the most handsome character in the story completely interrupted everything to explicitly tell you not to.”
And you've been reading in on our little conversation here. It's in somewhat poor taste to address you directly, but some things are more important than the fourth wall. One of those things is your personal safety and well-being.
We're about to talk about Eleven Jones Cave. This is a cave I live in, but I can only do that because I am unkillable. If you're reading this prior to the year 2026, you are extraordinarily killable.
Do not attempt to enter this cave. I say this for two reasons, the first of which is that there is a very real risk of you getting stuck in it. The second, and more important, reason is that this cave harbors extraordinarily high levels of carbon dioxide.
I know how people are. Maybe you're telling yourself, "well, I'm special, I won't let myself get poisoned by carbon dioxide." You will, and you'll be remembered as the person who died in some crappy cave because you read it in a story you read online about sentient 178th-century space probes who watch football all day, even though the most handsome character in the story completely interrupted everything to explicitly tell you not to.
There are a few novels that use footnotes as a conceit. Mary Gentle’s The Book of Ash comes to mind. In Nabokov’s Pale Fires, the editor adding footnotes is a character of his own with an unreliable point of view, but the best example I can think of is actually a non-fiction book. Some editions of Edward Gibbon’s Decline and Fall of the Roman Empire, including the one on Project Gutenberg, have multiple dueling sets of footnotes, where Gibbon himself is often more witty and acerbic than in the main text, and the commentators are arguing with each other, particularly about Gibbon’s views on organized religion.