Boil it in water for a few minutes might help as well.I had bought a replacement grommet and the vendor suggests to place a socket through the grommet to spread it. A socket just big enough for the speedo cable head to fit through. Some dawn dish soap or lube may assist as well.
THIS, is the solution I'm going with.. Didn't even know they came with pre-installed grommet.Why you buy a cable with it installed! Otherwise the only real option is to slit it and put it over the cable, or find a gynecologist with some spreaders...