I vote stairs, but turn them 90 degress, so they run parallel to the building edge. Looks a bit awkward with them sticking so far out from the building.
Alternatively, if you want to avoid jumping, but still use the boxes idea, can't you cover them in a ramp-shaped brush. Then make that brush invisible but solid. I don't know the name, but I'm sure there's a brush material designed specifically for this kind of thing. That way, the physics sees a nice smooth ramp that follows the rough outline of the boxes.
EDIT: What Jazz said above, whilst I was typing (for a long time...!)