Extra kidney or liver to augment actual organs.
Instead of replacing organs you could have these as extras that you could hang on before going out on a party night or before a bachelor's party. Then he could drink yourself silly and still have filtered out really fast.
Along the same lines if you are feeling kinda rough in the morning after a an exceptionally long drinking session or drug session or whatever you could hang on an extra filtering organ and get the stuff I your system a lot faster.
