Speaking of Simon...You can also make an wedge shaped shim out of veneer. Each layer of veneer is 0.6mm. Figure out how tall it needs to be at bridge-ward screws and then taper until you get to the nut-ward screws. I found it hard to figure out the exact angle I needed, and this let me experiment with different angles without breaking the bank.

Years ago when Simon suggested one of the MANY uses of veneer in woodwork and luthiery, I bought a 1x2 foot piece. I have used it many many times since spending about $5 on it, and still have most of it. This is one of them ;-)