Controlled block corruption testing

I'd like to do some block media recovery testing in RMAN. It seems that the Linux/Unix "dd" command would be an obvious choice to corrupt an Oracle datafile block, but has anyone documented a controlled test like this? Try to not reinvent the wheel, if possible.

I'm thinking of targeting specific objects in the database to corrupt. It doesn't seem difficult to get a relative block and "dd" an empty block in its place on a test instance, but if someone's already beaten this path...