if he's being sensitive, you could try putting the neosporin with pain relief on his ear about a half hour before you want to test, then wiping it off when you test. we slathered it on punkin's ear every night and they seemed like they healed overnight. that combined with making sure to apply pressure and stop the bleeding after the poke was enough to prevent scar tissue.
have you ever used it the neosporin with PR on yourself? punkin gave a giant leap off my lap one time (hehe there was a can of food being opened in the kitchen and he launched right off of me) and thoroughly scratched my legs, so i tried it on the scratches. completely took the pain out. it is amazing stuff.
i know some people are fans of footpad testing - i would be concerned about germy litterbox issues. but ya gotta do whatever works!