A bit of an update. The course of antibiotic is over. Last night he was trying to push the growth off with his pectoral fin. I felt bad for him so I grabbed some tweezers and netted him. The growth was about 3/8" long at that point. It broke off when I netted him and I was unable to find it. There was a bit of a stub left so I dug it out with the tweezers. It was really not impressive. What I pulled out was very small and an opaque white color. I was kind of desperate so I soaked the area with metro and salt as I held him before letting him back in the tank. He didn't seem any worse for the wear and this morning no growth was there. It usually takes a couple days to see the lump again though.
On a sidenote, I went to a reputable lfs today to get Prazipro in case it is some kind of worm. The owner checked out the pics and said he hadn't seen anything like it before but noted if nothing is stopping the growth it may be some sort of fast growing tumor.