Did he say to stain it first and then shellac or just don't mix the two Steve? And would it make a difference if the stain was oil based or water based. There is also some alcohol based stain, although I've never tried it. Since the shellac uses alcohol for a solvent then that stain should be able to bite into the shellac.
Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.