Disable all quests. There're some quests allowing "irregular" ways to earn XP.
Disable grouping. Else, it'll be just like Bori - several zergs form, largest zerg wins, others quit or join, end of story.
Only allow players to earn XP for one hour per day. Else, it'll just be a "race" of having no job / family / other hobbies (and take about three days).
Having made my three suggestions: I think it's a stupid idea. Even if no developer time is needed for that, even if it doesn't cost you a dime, even if it takes an hour or less to implement - that hour would better be used on something else. Make a video contest. Do a guided tour through T1 and T2 for new players. Spawn Hathor-Ka in Paikang in front of T4 (or, if you're really funny, in Tortage).