Maybe pull the plug on each injector, while the engine is running? The one that doesn't make a change in the way the engine idles is the culprit. Just a guess.
The CBT is the best thing you can do (way way more accurate than listening for a difference when a cylinder is disabled).
Otherwise, you'll have to pull injectors. Make a rig that connects your air compressor line to an injector. Set the regulator to 40 PSIG. Place the tip of the injector in a clear plastic cup with water and a couple drops of soap in the water. Turn on the regulator and see if your injector makes bubbles. If it does, it's leaking.
Lots of times yuo can just put a screwdriver up against the body of the injector and feel the injector pulses via the screwdriver when the car is running. Find the one that isnt pulsating or pulsating less than the others and there you go. This doesn't work on all styles of injectors as some will give very little vibration to you where as others will give a lot. I haven't tried it on our cars so i couldent tell you if it works or not. But it only takes like 10 sec. to find out....
Also you could try some fuel injector cleaner...worth a shot.