Perhaps you should re-read what the Maintenance Schedule says about the Wheel Bearings. It doesn't mention "Grease", it says "inspect Wheel Bearings". If you look in a service manual the procedure for Wheel Bearing Inspection amounts to measuring the deflection of the hub, I think the limit is .020".
There are no grease fittings. The bearings, while not sealed, are not intended to be serviced. The inner seals can be replaced but the outer seal can only be replaced if the hub is removed (destroying the bearing). If the hub deflection is out of limits the bearing should be replaced.