You may want to try this workaround that I tested successfully. First, I enabled plus addressing on my account that I'm sending from and want a copy of the sent item. In the event, whether you want it at the system level or the user level, modify the "add recipient" action to use that plus address. For example, I added "email@example.com" as my recipient address. I received successfully a copy of this sent message in my sent items folder.
The problem is that the user will receive duplicate copies of the sent item if they use webmail or a client that automatically saves a copy in the sent items. Unfortunately, there is not a workaround for that that I can think of.
Hopefully this helps!