The other issue I had was that it was not immediately obvious to me how to add a Boundary Event to begin with. I tried adding from the palette but instead of dropping it on the border I was trying to drop it on the task itself.
I actually thought it was just not supported in the modeler, until I received confirmation from another Camunda user that you do indeed have to drag from the left which gave me more confidence to try different approaches. Silly me.
However, I wonder why not allow the user to drop it in the middle of the task and automatically pop it to the border (anywhere)? Also wonder why it's not added to context menu.
You could also change the tooltip on the palette to say Create IntermediateThrowEvent/BoundaryEvent.
Just some ideas.