Command Line Parameter for "open in existing Instance"

I'd like to open a new tab in a running instance of explorer++ from Command line.
I didn't see such a param in "explorer++.exe --h".
I am aware of the Setting "Allow multiple instances" (which I have enabled), but I'd like to control that when running the exe.

Is that possible?

Is there a doc of all command line parameters somewhere?
explorerplusplus.com gives me a 503 error currently.
