I don't get why people could possibly get addicted to that game! I started off on that training island and was wearing some sort of apple suit. That was the tipping point in my case, a total play time of about 3 minutes.
Anywho, to get him to stop playing, I see there are two ways
A mental tactic: Tell your dad or mom, that he's not doing (insert thing parents always bug him to do) and that its because of maplestory.
By force: It seems deleting his game/character dosen't help, and trying to block the website may not work, there's probably a mirrior out there.
I suppose you could do some sort of hack that breaks the game on startup (no matter how many times it's re-installed).
I've thought about this, and it seems he has a real addiction. The only thing I can think of (That would actualy work) is getting him another game to leech off of, preferably console. Maybe getting him ip banned (loveual harrasement ftw) would do the trick.
Well, I've just used up my mental energy for the day