If you have it, the Cash Balance Answer Book shows exactly how to convert the contribution credit/accrued benefit to an equivalent contribution. You may be able to restructure and pair old NHCE with young partner, testing on contribution basis, and older partner with younger NHCE on a benefits basis.
Yes, you can test a DB plan on a contribution rate basis by using the present value of the increase in the accrued benefit.
This however you can't do. Your actuary is correct. A CB pay credit is a hypothetical allocation.
I don't think Lou needs a cite in this case. If someone wants to claim the terminated over 55 exception applies to this plan and not the original plan the burden is 100% on them to prove it.
The plain reading of the rules gives no reason to think that exception "sticks" to the money.