Something like that might just work.
Someone else also suggested Q-boats, heavily armed vessels disguised as helpless merchantmen to ambush the pirates. This has the additional advantage of making trials unnecessary. Again, you don't need a foolproof system, just enough to complicate their planning and increase the risk/benefit ratio.
At any rate, I just heard the good news about Capt Phillips' rescue and I'm celebrating. Hopefully, this action, plus the French storming of the yacht taken by pirates, may just signal the turning point in this sordid little episode in maritime history.