Ina found an interesting video on YouTube a while ago that talked about turning the cherries from Cornus mas (European cornel / gele kornoeille) into something resembling olives.
We have discovered three Cornus mas in the park nearby. This year the trees had a mast year. Naturally we decided to try this recepe ourselves.
We made three jars at the end of July. In early September, I discovered one had started to ferment. We have transferred that jar into the refrigerator and we are eating the cherries. They do taste like olives!
The video linked above makes the suggestion to replace the water with olive oil after the resting period. We have not tried this (yet).