Picatinny rail for S&W 19 revolver

I recenly purchased a red dot sight for my air pistol. My shooting experience with that sight has made me a believer in red dot sights. So I am considering getting one for my S&W Model 19-3 revolver. But I want to keep my iron sights on the revolver. (You never know when a battery can go dead.)

Before you ask, yes, I know I'm going to have to take it to my gunsmith to get it drilled and tapped, or whatever, to mount a picatinny rail. What I would like to know is if there is a rail solution that allows me to keep my notched rear sight on my revolver while a red dot sight is also mounted. I want to be able to quickly revert to using my iron sights should the red dot sight fail. Which means the sight line between the front and rear sights cannot be blocked.

What I've read so far involves removing the rear sight and using that area for part of the mount for a picatinny rail. I would like to avoid that. Any ideas, anyone?