Replacing the ball joints?

I am replacing the ball joints on my '96 Outback Wagon, 4 cylinder. I removed the ball joint from the steering knuckle and control arm, installed the new one on the control arm, but cannot get the new ball joint back into the steering knuckle. I greased it a little, pried on the pinch slot some, but can't get in. I'm afraid to hammer on it too hard for fear of breaking it. I pressed on it with the jack, but backed off because I'm afraid I'll push the car off the jack stands. Will it damage anything if I lower the car to the ground and try to let the weight of the car push it into the knuckle? Or do I just take a big hammer and pound on it until it goes in? Do you have any ideas or techniques?