I would think if preventing the billionaires' wet-dream of a constitutional convention were desired, either New York or California or some other large, rich state, in their legislatures could say, before that appalling threshold of risk is reached that they won't guarantee to enter into union with such a new nation formed under one.   And that any such decision is so momentous they wouldn't agree to it unless it was the choice of a popular vote of the Voters, not the various state legislatures, there is no reason in the diverse 21st century to go along with that 18th century, world of property owning, white, Christain men means of adopting a new constitution.  I would think that would limpen the wick of the billionaire boys club. 

If I were a member of either legislative assembly, I'd introduce a bill to that effect as soon as possible.  Since I think a horrific civil war would be the likely result of such a con-con, someone should look into doing that, not to mention the desired results of its patrons, corporate feudal oppression.