Um, and how exactly do you propose to match the IR signature of a real ship, without building what is essentially a second ship?
"...Um, and how exactly do you propose to match the IR signature of a real ship, without building what is essentially a second ship?..."
I don't. If the decoy is close enough to the ship, it shouldn't matter for missiles fired at the waterline. In any case, it should be possible to build an emitter that replicates the signature of the main ship. Spread a dozen or so of these in the area, and it should confuse missiles.