How do you automatically derive an instance for a data type defined in an imported module?

-- automatic instance derivation directly after type declaration
data Val1 = V1 Int deriving Show

-- manual instance derivation can be in separate file
data Val2 = V2 Int
instance Show Val2 where
show (V2 i) = show i

-- Is something like this possible?
data Val1 = V1 Int
...
derive Show Val2

Thanks,
Greg