Here is an impressioning handle I made a while back. It works fairly well, but being solid steel, it is heavy and can easily have too much pressure placed on the key during lifting. A little practice and it worked fine. Just happens I was at work when I made it, and the steel was free - part of a broken part.
The aluminum mentioned above would be better since it would you allow to feel the key and pins better. The set screws can be the same, holding the key very firmly, though it leaves marks on the key bow.
Normally don't give an impressioned key to a customer since the key would be weaker due to the stresses of impressioning. I duplicate a copy to a new blank.
Gordon
Just when you finally think you have learned it all, that is when you learn that you don't know anything yet.