well my friend i wish someone could dream up a soloution , i work in the drilling idustry and this situation is honestly worst case senerio. there are several factors that make this so difficult to overcome . #1 the water depth 5,000 feet of water there is no machine to my knowlegde that has been devoelped that can kill a well at that depth, there are many on land and offshore . #2 the rig debris on the ocean floor. #3 the marine riser thats conected to the bop stack. #4 gas migration in the oil freezes iron and steel which with the water temp at that depth has frozen every movalbe object there. if they go in a shoot debris in the well they can also kill it .but its very diffuclut without a rig or platform there. the cement block theory is a good idea but it would take a block the size of a building to overcome the bouyncy factor of the water to create enough force to smash the pipe.