[Haskell-cafe] SYB: extending a generic reader with a type class

Dear -cafe, Is it possible to extend a generic reader (extR / ext1R from syb) with a type class? For example, let foo :: (Integral a) => SomeMonad a I could write: reader = ... `extR` (foo :: SomeMonad Int) `extR` (foo :: SomeMonad Integer) However, that is tedious. Could I do something like reader = ... `extR` foo and have it apply to all instances of Integral? I hope I am being clear. Thank you.