The way I currently do it - I bike back and forth on Route 7 gathering eggs and boxing them 5 at a time. When the box fills up, I go to Lumiose city and use hatching power 3 to burn through the 30 eggs.
Is there a more efficient way to do it?
Your method is pretty much perfect, the only problem is you should use a Pokemon with Flame Body to make the eggs hatch faster, like Talonflame (it also gets Fly so it's extra convenient).
EDIT - also, the Oval Charm makes Pokemon breed faster.