u farm the troll. the person getting levelled sits back and watches just in range to get exp. the best way to do this is to attack a troll once then run and stand quite far back. the person can also use scrolls to speed up the levelling process.
I assume you're W/Mo, but as a 55 monk, I throw Berserker's Insight (gold 30sec 3x xp) up just before the trolls start dying, and make a handy bit of xp.