In diagrams.net, create "connector with symbol" with custom shape

Pretty recently, in the "General" section of shapes, the "connector with symbol" was added.

I was able to replace the email symbol with built-in shapes by editing the "Style" of the shape and setting shape=message to shape=cloud, for instance. But custom shapes (shapes in the Scratchpad) can't be referenced this way.

Now, how do I replace the pre-defined email symbol in the connector with a custom shape?

Example:

How and where did you create a custom shape? E.g if you take a custom shape described here:https://www.diagrams.net/doc/faq/custom-shapes, add it to canvas, press Ctrl+e to see the code, copy all shape related lines after "shape=" and paste it into e.g message shape, you should see message shape replaced with custom one.