achosid: As far as I know that is an incorrect take on what’s written about the Gaon.
All it says in Ma’ase Rav is that The Gaon would try very hard to taste chometz motzaei chag, and would avoid eating matzah (that one can eat to be yotzei the mitzvah on Pesach). It then says that all of this was a heker that everything is being done for the mitzvah (to do what HaKadosh Boruch-Hu was gozer) and not for enjoyment.
If you know a source to the contrary, however, I’d be interested to see it.