Don't think this is a new idea - there was talk of using concrete-filled PGMs a few years ago - I think in relation to Bosnia: land 1,000lb of concrete on a tank, and you'll make it difficult for it to pass its MOT, but won't hit nearby civvies or Culturally Unique National Treasures (a phrase that was abandoned about thirty seconds after it was coined...). The most recent references I've seen to this have been about using the training rounds or a deriviative glorying in the name of Minimum Collateral Damage Weapon.