The 1.8 definitely does not mount with any current Nikon S/Contax to Leica adapter. But there a few people out there (I know of a guy in S. Korea) who can modify it so that it can work with the adapters and still work with the Nikon S. Other people like Skyllaney made new lens housings for the lens to fit on a Leica -- but this was a permanent modification. A guy in Japan whose name I cannot remember would do rather crude Leica conversions that rendered them incompatible with the Nikon S. I am pretty sure he does not do them any more.
I believe the story was that Tom A requested that the Bessa R2S be developed so that everyone could use lenses like the 1.8 and the 21mm f/4.5 Biogon on a modern rangefinder.
But for those who really want the 1.8 experience in a lens that actually works with a Leica, look at the Konica UC Hexanon 35mm f/2. It replicates the 1.8 very closely (has almost the exact same design), has the same minimum focus (0.9m), is a beautiful brass-body lens around the same size as a Leica IV Summicron (actually the Hex is a little smaller), and is still cheaper than an OEM 1.8 in M39. While the 1.8 has better barrel distortion control, the Hex's coatings are modern and are substantially better for color film / color digital. Both lenses focus shift in the exact same way.