Since the 35/1.7 has a 39mm filter size and externally threaded small round hood, like the 35/2.5 Skopar C, I suspect that the LH-2 shade will fit the Ultron as well. I don't know if it may cause vignetting on the faster lens, but it should fit.
I've also noticed that Leica clip-on hoods like the 12585 and IROOA can be mounted on the 35/2.5 Skopar C (and the 50/2.5 Skopar). If the front rim on the Ultron is, in fact the same, you might be able to mount a square shade for the 35/2 Summicron.
Finally, it might be possible to mount one of the vintage Canon clamp-on shades intended for their lenses with 40mm filter size. There was a square shade that might work for you.
Good luck!
Ari