[color=darkblue]MY TWO PESETAS...
Really, I think too many people get caught up in the idea that you need to make every squeeze of the trigger some operatic slo-mo visual poetry.
Despite what the book says, there's nothing wrong with saying, "I shoot him."
My crew likes the game, and almost every one of the PCs carries a gun. But they enjoy the overall action, no the specific action of firing a gun. It's cool if one of them wants to try a stunt, but more often then not, they simply decide to "fire my Baretta at the guy in the kimono," without worrying about making it into some stunt-infested romper-room style pandemonium.
I guess my point is, don't sweat making up gun stunts. If one comes to you, great, if not, just pull the friggin' trigger. One of my player's PCs is also a Killer, but he's a low-ranking exiled Yakuza trying to make a name for himself in the U.S. He focuses on looking good, and making witty remarks, more than trying to dream up a stunt to shoot someone.
If your player wants to play a killer because he likes the archetype, then he should just do that and have fun. There's no reason at all that he has to use a gun all the time, either. He can make up all sorts of hand to hand stunts. Just because he's not as adept as a martial artist in melee doesn't mean he can't try some cool stuff with his hands.
Also, the definition of the "Guns" skill covers all ranged weapons, not just firearms, remember. Specifically, if you were an archetype from an ancient juncture, you could choose "sling" as a weapon. I'd easily allow this sling idea to be applied by a modern PC. Wrap a cue ball in a towel, spin it, chuck the ball at someone's head. That's a Guns roll right there. (Martial Arts is used to throw stuff, but I don't count slinging as throwing.)