I don’t know if it would work but I was thinking of something along the lines of a cofferdam. Something that would fit over the whole assembly at the bottom lowered in narrowing segments until it reached a point where the oil and water could be pumped off together.
I agree with the cofferdam idea. But I would make it about 50 taller than the top of the BOP that is in place and then pump hydraulic cement into it. Fill the whole thing up and it would choke the well.