How brave are you? Tap rear sight out, left to right referrenced to the rear and looking forward. Jig it up carefully in a machinists vise and drill a 3/32 dia. dimple on either side of the notch. Degrease and fill with some white lure paint or fluorescent paint. Granted, amatuer approach but if you do a good job no one but you will know.
Tap in back in from right to left. Most dovetails are oriented that way. Don't use steel hammer or drift, use brass or nylon.
Good luck.
btw If you don't like the job you are back to square one and can take it to a gunsmith. My Walther has 3 dots and I like it that way.