Based on JohnZ's tip, I had a taper tool made out of Nylon and it work great. As shown, it fits inside the speedometer end of the cable. Lithium grease was applied to the tool and over the cable. I fixtured the cable in my vise and the grommet easily slipped over the cable by hand. I would recommend that you apply a light film of grease over the length of the cable to help slide the grommet into location.
Push the grommet past the approximate location it will be located once the cable is installed in the car. After the cable is installed, slide the grommet along the cable and snap into the firewall hole location. Wipe the cable clean. It's very simple!