I don't know how to make IR's, but if it's based on a sample, then do this:
Get a large glass, or a pot, and fill it with water. Get a straw and blow air into the water to make bubbles. Sample that. Use that as your IR.
If you need bigger bubbles, remove the bulb from a turkey baster and blow into the narrow end, wide end in the water.
Again, I don't know if you make IR's with samples, but if nothing else you'll definitely get an "underwater" sound that way.
Another suggestion might be to take your bubbles sample, pitch it down slightly, and use it as the modulator in a Vocoder.