Well, Mum, maybe the thing to do is to play it absolutely straight. Give Dolohov a nice shiny plaque with absolutely no charms upon it whatsoever. Or...come to think of it, maybe you could give him that chess trophy cup that he won at that summer tournament he went to with Dad after his second year. Won the Devon Junior division, I think. (You didn't get rid of that one yet, did you Bill? He used to keep his cufflinks in it.) You could ask to have it displayed on a plinth in the trophy room, with a marker: In Memorium: Percy Weasley.

AFTER Dolohov has run every test on it that he and Barty Crouch can think of--they can tie themselves into knots over it, but they won't find anything. If we're lucky, they'll decide to humour you and display it there.

And then Professor Dumbledore or Professor Sinistra can slip in afterward and add something to the base. It'd be easy as anything for the Transfiguration Professor to create a hidden compartment to the cup's base, maybe set so a password can open it. We could stash whatever we think's best in there, and then tell the Galleon holders, 'If you're in trouble and you need 'X,' you can grab the Percy Weasley cup in the Trophy Room and say, 'Doloros Umbridge has thunder thighs,' and it'll open up the back of the cup base.

And there you have it.