Oddly enough, I ran into this problem last week with my M7, when we had our son's birthday party. No way to take family pictures without a self timer. I had to resort to my Nikon F3 instead of the Leica.
There are third party self-timer makers. I had one by Knirps. I think Kopil also used to make them. They are relatively inexpensive on ebay. They thread into the cable release socket on the shutter release.