Here is my humble contribution for a possible way to cap/contain the oil leak. Kevlar 149 is very tough stuff. The info I could find says it’s good to about 27 million psi tensile modulus which I would hope would be enough to contain the oil. My idea is to have a short custom riser pipe fabricated with pads to anchor hold-down chains and a short steel cone on the bottom to align the pipe over the existing riser. A tight fit isn’t required.. because over the whole connection is a Kevlar sleeve that can be cinched under the existing pipe flange that is just under the now cutoff riser. I would also wrap the flange in a tire to protect the sleeve from the sharp edge and help seal the connection.