I don't think that works. I'm not an SEC regulator, but I don't believe there's any requirement that the brokerage hold real shares for the full total of all o

I don't think that works. I'm not an SEC regulator, but I don't believe there's any requirement that the brokerage hold real shares for the full total of all outstanding sell orders[1], or to logically segregate the holdings of different customers. If someone comes by and tries to buy that million dollar share, the brokerage is merely required to honor the trade with a share they have from anywhere, including one purchased from the market or held by a different customer. Again, this whole notion of "Hold the Line" is just not how trading works. [1] I mean, that's just trivially violated by a perfectly normal short sale by definition.