the problem with wedges is that it will cause misalignment and shearing action on the bolts used to hold the ball joint on. Not really ideal, I cut the mount out of my upper arm and weld it in a new one.
also putting a wedge in will increase the angle of the upper arm and depending on how low you want to put your car you will end up with your upper arm binding against the tower. From here you can machine the back of upper arms get more clearance.
if you are going to wedge make sure you try to do it so the top and the bottom of the bolts are bolting on a square surface, you may achieve this by wedging the underside of the top and bottom of the bolt by equal and opposite angles, and it should be fine. make sure you use high tensile 8.8 or 10 grade bolts.
The better option is to purchase upper arms that are already modified with angles to correct ball joint binding these exist and are cheaper now than they were when I had to make my own arms.