If you add a keyboard shortcut to Scope Box - it doesn't work in the Family Editor...
If you add Scope Box to the Quick Launch toolbar - guess what? The Scope Box tool suddenly 'appears' in the Family Editor - but it is always greyed out. Remove it from Quick Launch, and it disappears just as suddenly... check it out:
How are we going to get around this one? Simple - use this method to transfer a Scope Box from the Project Environment to a family RFA. From there, we can copy the Scope Box from family to family as needed!
Here is another gift from What Revit Wants - a Generic Model family with a Scope Box in it that you can copy to other families:
It's pretty funny that you can't even Create Similar once you have a Scope Box in the family!
EDIT: Added video showing creation process: