I see several solutions. You could use tie to change the stringification of your coderefs (I think). You could just emit code to chage the DUMMYies after the Data::Dumper generated code. You could do some sort of parsing of the Data::Dumper output. You could write the thing yourself. You could use another serialization provider that /does/ provide the ablity to hook into it. You could use the Toaster or Freezer methods of Dumper (though I'm not sure how well they'd work for you).

Oh, bingo: See the examples section of the docs, and the Seen method.