How about addiing one hit kills to the trainer.

You could just give gun damage enough of an increase using badass ranks in the editor to oneshot kill anything regardless of if you're using the trainer or not.

The purple guns that you get from the golden chests usually do like 25,000 points of damage or higher. You don't really need a one hit kill option when you have a gun like that. Plus, you can increase the damage a gun does too.