can you please give me an example of why you would set up your pipeline that way? Why not create a sibling stage with nested stages? It seems unnecessarily complex.
The question you should be asking is "why are we creating arbitrary restrictions ?".
Restricting actual functionality for the sake of easier visualization in Blue Ocean is not an answer you should find acceptable.
The fact that you see a pipeline as unnecessarily complex doesn't mean that it is, or that it's wrong, or that it should be prohibited.
If you're having trouble with presentation, look how TeamCity does it - it can present any pipeline you can imagine, with no issues.