Like this:
Context_Menu_Shortcut.png
open the group/component and select a face only
go to 'Preferences/Shortcuts' and filter on 'select'.
grab this bar and drag right to view the full menu item name (you can't modify the Preferences window size itself)
select the 'Bounding Edges' item from the list
enter your shortcut
The main thing to remember is that to add a shortcut for a context menu item, you must be in the specific context that loads it into the context menu flyout (you can check that by right clicking and seeing if your desired item shows up in the flyout: if not, you're not yet in the proper context). Otherwise it won't show up as an option in the 'Shortcuts' list.
It's not obvious that it works this way, but once you understand how it works it does make sense.
Hope this helps.
Doug