Its been said in the books more than once that the only way to get rid of them is to willing let go of the coin.
Not just that, but Micheal said that Harry would have to give up the coin AND all of his magic power (the thing Lash was using to tempt him) and never use them again. Only then would he be rid of the shadow. Lash self sacrifice was a way around that.
Also, unless the "Fallen touched" has instituted a way to block the coins power (as with Dresdens circle), then the shadow isn't cut off from the Fallen, and can draw upon all of its power.
All in all I'd say, a PC just whipping up a spell to get rid of it would be impossible. It would severely reduce the powerlevel and creepiness of the most powerful monster in the game. If such a spell were possible, no one would ever need to worry about the coins again.
If you want to end the whispers of the fallens shadow, you have two options. 1) Throw away the coin and permanently forsake the thing the Fallen was using to tempt you. 2) find a "plot device" level NPC to do it for you, and be ready to be ITS bitch for eternity instead.