ELmer & Salome: Boundary vs Body

Big Thanks for all the help.
I couldn’t have gotten ahead without advice I received on this forum.

Fred has been a saviour!

My question: Groups created in Salome appear as Bodies in a FEM called Elmer. For exmaple, like this…

…becomes a Body.

To make a Boundary out of this, Elmer tutorial on Salome suggests using
Mesh>> Face groups separated by sharp edges. But that’s useful for shapes like squares, I think.

How can I achieve the same for the geometry object shown?

Thanks & regards.