A good stock 'smith can extend the lop by adding a piece. I've seen some done by top drawer workmen that were almost undetectable, others that were hideous. Key is a good 'smith. It won't be cheap, but should not be four figures either. Part of the job is hollowing out the stock such that the dynamics don't change much.

I agree w/ others here that a pad is a really bad idea on a gun such as this. It will badly imbalance the gun (pads are heavy).