Would that actually work in LivingUpdateEvent? There is a lot of stuff that is updated between when your code runs and when the xpOrbs do their thing in onCollideWithPlayer. Depending on what is updated there might be a difference in what orbs you collide with and what orbs are actually picked up.
If you are targeting 1.7.2, I'd add a hook to onCollideWithPlayer that fires an XpOrbPickedUpEvent. If you get it pulled now, it'll be in when the recommended build is set. That way you'll be all set going forward, not to mention any other mods that may want to mess with xpOrb pickups.