Easiest way is to unplug all of the fuel injectors from their harness. That way you have no fuel being wasted in any cylinder. Spark won't make a difference in the other cylinders you aren't guaging the compression on, so you only need to remove the coil on the cylinder you are working on when you get to it...
I first pulled all the plugs to allow the engine to spin more freely and I unplugged the injectors so none of the cylinders would flood. I then screwed compression gauge on to each cylinder and allowed the engine to turn over a good 5 to 6 times to read max pressure in each cylinder. I went all the way around the banks again to get a second reading. I then added a small amount of oil to the cylinders that seemed low to check if it was a valve or the rings (the extra oil will temporarily seal the rings).
I recorded everything I did as I went and my friend who was helping me watched the compression gauge as well to double check my numbers.
I think I was very thorough in the way I performed the test. I think I will have time tomorrow to give it a try again and see if the numbers are any better.
What temp should the engine be when I do this again. Last time it was warm but not hot because I was unable to pull the plugs when it was fist shut down. And does the outside ambient air temp matter?