Enable "remove" button on opportunity subgrid

I have created a custom entity that can be related to many opportunities. Sort of a "parent" opportunity so to speak.

On this entity I show an opportunity subgrid showing all related opportunities.

Now, I had two problems:

1. I wanted to hide the "delete button" for selected records in the subgrid because the users thought that it was a "remove" button but they actually deleted the opportunity. This was solved by removing the "delete" button from the subgrid.
2. I want to show a "remove" button so that the relation to the opportunity can be removed directly from the subgrid on the custom entity form.

Now, the issue is that I can see a "remove" button on the opportunity subgrid in the ribbon workbench editor but I can't figure out how to make that button visible on the subgrid.

So the question I have is therefore: how do I make the "remove" button display on opportunity subgrid when the subgrid is displayed on the form of my custom entity?