Here's a little something for folks who have a Dusheck Slippery Sam set, one of his Ultimate Copper and Silver Transposition sets or the Digital Dissolve product from Theory 11:
If you wear a pocket square in your jacket and want to bring that item into play :) recalling the Ramsay routine...
Get set into the position where you've got what they think is the silver coin in a cup or in one person's closed hand and have the gaff in hand showing as the copper. Now bring out the pocket square and ask for a volunteer. Cover the coin at your fingertips and ask them to pinch the coin to confirm that it is there. Make an indirect display of both hands otherwise empty and display the apparent copper coin at your fingertips and let them cover the coin with the handkerchief. Let them take the coin from your fingertips as you instruct them to hold it tightly. this might be a fun moment to get out a glass, quietly lose the gaffus, and when the moment is right have them drop the coin into the glass. What's left in view is innocent and leaves all the wrong clues for those who like to guess.
A less audience centric approach would be to parallel the Ramsay two coin transposition using black and white hanks by way of a misleading display to have them infer that the silver coin is going into the white hank and later on rotating the coin at your fingertips to permit the gaffus to get free of silver coin.