You do not need an FFL to perform cosmetic work on firearms. Engraving, painting, anodizing, etc etc. That’s not considered gunsmithing. Taking possession of the guns for the work can be illegal pending state but doing the actual work in front of the owner is not
I do not engrave receivers or frames because I do not want the liability of having to replace/repair it if it gets screwed up in the machine.
You may want to contact the owner of Lock Stock and Barrel. He may know someone that might hand engrave this for you. I remembered about him after we got off the phone the other day…