That ability is finally here!
Check out Config->Forms->Customizable Manners/Affidavits and you will see an Email link there you just open it up and check the box to use it and put in your custom email for that manner!
We have a customer putting in his skip-trace prices on non-serve emails that were bad addresses so the client can decide then and there if they want our customer to skip the defendant.
For Diligence manners you could have all attempts go to the client in the auto-completion email as well.
This looks to be a powerful feature! We will be adding things to it, let us know how you like it!