Does your current hammer have a threaded hole for an extension now??
If so find the thread pattern and size get a small aluminum rod tap to fit and cut it to length paint to match. No need to mod the gun itself.
"Gun control: The theory that a woman found dead in an alley, raped and strangled with her panty hose, is somehow morally superior to a woman explaining to police how her attacker got that fatal bullet wound." — L. Neil Smith
The problem with being stupid is you cannot simply decide to stop doing dumb things...
"I crapped my pants to avoid the draft!!" -Ted Nugent