I did a search for "Keyboard Shortcuts" within the CA Plex IDE's online help, and found an article titled- take a guess- Keyboard Shortcuts. It lists the keyboard shortcuts for all of the main components that we use in the IDE to design our Plex applications, and yes, it does include a section on the Action Diagrammer keys. Unfortunately, there is no keyboard shortcut documented for the capability that you need.
So I recommend adding this to the IDEA wall as an enhancement request if you think this would be useful.
Thanks,
Stephen