Can you block mods on a vanilla minecraft server?

Ok, so I run a basic multiplayer minecraft server to play with some of my friends, but lately I've run into an issue. I've got this one friend who can be kind of a jerk at times, and he recently figured out how to install mods. He keeps getting more and more mods, and I really need to block some of them. First he had inventory hacks, which made him invincible, and also he just got an x-ray mod so that he can cheat to find dungeons, diamonds, and so forth. I tried to make my server into a bukkit, but it didn't work right, so I was wondering, is there any way to block mods without a bukkit server?