First, construct a form and drop it so that it surrounds the wellhead (or whatever it's called). This would need to be a little bit higher than the "plumbing" from which the oil is now pouring.
Next, lower a pipe roughly the same diameter as the size of the leak directly over the opening, and just start dumping dry concrete inside the form until it completely fills the form. Yes, concrete will set underwater.
Let the tankers queue up to capture the oil.
Obviously this is an over-simplification of what would be needed, but seriously...how difficult would it be?