Just put a jack under the lower wishbone ball joint and jack up until the weight just comes off the axle stand. That should set the wishbone in the position it'll be in with the weight on the wheels.
I tried the hammer method on the lower ball joints and failed miserably, obviously didn't have the knack. Just ended up denting the bearing housing. Even the scissor splitter I bought struggled and ended up banana shaped only finally springing one joint after a smack from a lump hammer. The lower ball joints were the worst part of the job in my case.
I've got a 40 oz mechanics hammer, its helpful if you can be underneath the car so you can give it a good swing. Upper balljoints usually pop on the 2nd swing, lowers on the 4th or 5th although you do get the odd one thats trouble. You do get the knack of it after you've done a few. If you're doing it on your knees its harder to get the power in the swing.