That's pretty funny, but now that I see it, I agree its silly.
Personally, I'd rule you only get the damage for entering a damaging zone once per full action of movement (where a push, pull, or personal move action, whatever).
Scenari 1: I push someone 6 squares. Like that picture, I zigzag him in and out of the fire, so he entes it three times.
Scenario 2: I push someone 6 squares. The first square pushes him into the wall of fire; the remaining five push him 5 squares along the wall, never leaving it, so he's entirely within the fire for the full mvement.
In the first scenario, the victim spends about half the time in the fire but takes three times as much damage. That's silly.
So I'd rule as above: in both scenarios, the guy takes damage just once. If someone else then moved him out of the fire and back in, I'd be happy to let him take the damage again.