I'm curious why a copy of the invitation going to the tree-owner's e-mail is wanted? What purpose does it serve? The "Manage Invitees" section of Tree Settings tracks these quite well.
It seems to me what is really being asked for it the ability to set someone else up as a registered member of Ancestry without any input on their part - why is that a good idea?
I'm really having trouble understanding catering to folks who can solve their own problem but won't and yet want the benefits they would have if the problem were solved.