I don't personally own an Omega, but I have a couple of hunting buddies with them and I've handled them. I've never had much of a problem getting to the hammer. The hammer is fairly short on them, so it doesn't seem to be so much of an issue.
That said, I do have a Triumph which is fairly similar, and with a scope mounted in medium rings, it's not at all an issue pulling the hammer back. Even with gloves. I don't really see a reason to need a hammer extension.
You are right though about them not being drilled and tapped for one.