You need a SOOMP !! This is a special, rectangular hood that has an opening running across the top quarter so there is no blockage of the rangefinder and viewfinder.
There are SOOMP's made in Wetzlar, New York, and fake SOOMP's from Japan. I would imagine that there must be some sort of ring adapter to take you to a series hood, but I don't know what ring it would be.
Hope this helps.
Steve