I would agree that a single-piece new hammer with a built-in extension would be ideal, but it might require work to fit, since Ruger doesn't offer even a stock replacement hammer. How about an attached extension, like this one, at Midway?:
Carlson's Universal Hammer Spur Extension Aluminum
Copy and paste that into their search box. If needed I could put the actual web link here.
One of the reviewers used it successfully on a Redhawk.