Best way to pack rear axle bearings?

I assume you're talking about the factory style tapered bearings and not the "green style" sealed units... I use a "grease needle" on my grease gun and poke it into the end of the cage and pump the cavity full between each roller. Then spin the bearing a couple of times and repeat. After it's in and running, like Locomotion said; they're lubed by the gear oil. I just like to grease them on assembly because my stuff tends to sit around a while before it gets used... :)
Edit: Oops, yeah there are seals in the 8 3/4. pack 'em and pack grease behind the seal lips.