Can ungradable adjectives be used as gradable?

I was under the impression that ungradable adjectives cannot have comparative forms in any circumstances, because there are no degrees in those adjectives.

But I found a quotation from George Orwell containing an ungradable adjective "equal" and since then I wondered if there are other ungradable adjectives that can be used in comparative form.

"Some animals are more equal than others." (George Orwell)

The whole point of that passage is bitter irony: the revolution was carried out under the principle "All animals are equal" but is subverted when Napoleon's party assumes dictatorship and rewrites the principle :

All animals are equal, but some animals are more equal than others.

Logically and grammatically it's meaningless; but power trumps logic and grammar.