Soft solder an overlay of carbon steel to the top surface.
Veneering the surface was mentioned above already.
It solders easily with solder meant for use on stainless steel. Any Home Depot type store has it in small quantity rolls w/flux .
The thickness doesn't need to be much at all. Some thin shim stock can work just fine and conforms easily.
...or make an entirely new plug and fit it up.
Stainless won't fire blue or rust blue in any way that I have found acceptible,.
That real nice patchbox lid release I made one time,,all nicely fine checkered with a graver and all...nice and shiny brite stainless. Still is.