I shimmed my P bass with half a quality business card under the first two screws (bit nearest the neck). Worked perfectly and my P bass has never sounded so good, setup was super easy after that.
All I did was loosen the strings off a lot, find the correct sized screwdriver and undid all the screws, slipped the business card in then put the screws back in. Only had to screw through a bit of cardboard which was very easy. It added a little bit of angle which was all that was needed.
Found that tip on a website somewhere, and it was free!
I took it out again to see if it was a fluke and no it wasn't....