Have you thought of buoyancy bags?
One option might be to have bouyancy bags already inflated in unused portions inside the boat, and have enough ready to inflate to completely keep your boat from totally sinking.
Another option would be to have a set of bouyancy bags that would go on outside of the hull and be able to completely "float" the boat. You'd also need an air source (compressor), and dry diving suit (and gear). The type I'm referring to (for the outside) are the same ones used to raise a boat post-sinking, but could easily be attached before the boat goes down.
Whatever you do, do carry a liferaft and survival suits for everyone onboard. The lot on this sight would say an EPIRB is optional.
Please stay safe and think carefully about what you're about to attempt.
J/36 "Zero Tolerance"