Here is my trick:
Using 80 Weight Gear Oil. Add oil to a baggie and let sit for an extended period of time. Spin the bearings to help assist the oil penetration by moving the spindle inside the shell often.
This is not as good as axle grease, but you would never get grease inside the bearings using this method.
I also use a similar method to oil those suspension bearings that have the metal dust covers.