Put a 25.4 mountain-diameter bar in an old road-diameter stem. Tighten it enough to keep the bars from rotating, and SNAP! oops. Leave the bike in your garage for years.
I’m pleased – my friend moved from Portland to Petaluma, and now I can fix the bike I fixed up for her before. I turned her road bike into a city bike, broke the stem, bought a new stem and kept it in a box for YEARS. Jeeez. So now the new stem holds new drop bars, and the city bike is turning back into a road bike, but with fenders.