I know there are many stories about the Gedolim who “gave away” their portions in oilom habo for interesting things.
There was the story of the Gaon, who for some reason didn’t have an Esrog, and they went looking for one. The only person they could find would sell it for the sechar mitzvah of the Gaons shaking. The Gaon took the offer happily, and then smiled and said that it is his first time to be mekayem the mitzvah lishmah.