I like the idea of Echo just showing up completely unannounced. Maybe he could have been traveling with the arbites at the scene atm, which gives him a logical reason for being there.

We're becoming quite a lot in the party though. Maybe we might need some heroic scene or sudden danger for Zhevon to realize he needs that random arbite on his top-secret intergalactic campaign against heresy! :D 
Like valiantly saving him from a sniper's shot, or some other threat that I can't really think of because I haven't finished my coffee yet ^^