He means Anthromorphic by the way.
Here were my thoughts on it, though I'm not in the fight.
DMG, pg 89
For each 200 pounds of an object's weight, the object deals 1d6 points of damage, provided it falls at least 10 feet.
By the DMG rules, the eagle takes no damage as the boulder didn't fall 10'. Screwy, wrong, but the rules. However.
DMG, pg 89
Code:
Object Weight Falling Distance to Cause 1d6
200-101 20 ft.
100-51 30 ft.
etc etc
Looking at the first example we can see that something 200 pounds needs to fall 10 feet to do damage, so presumably, something 500 lbs or more wouldn't have to fall at all, just be set in place to do 1d6 points of crushing damage (if that seems small look at the minimum weight of a collosal dragon and it's piddly crush damage for sitting on something).
So logic and math could reasonably assume "Crushing Damage = (Weight/500)*1d6", or in this case, 20d6. Saves represent skill, luck, and ability, and I'm always against saying that something allows no save. So I'd say reflex for half. As for the DC, that's something that'd have to be case by case.
I'd make it flat DC 20 to shift your weight enough that when it crushes you it scuffs off a little causing less damage or have some blind chance provide relief...