You'll want to create a new "Ghost Parent" that is the top level subsidiary in the org. Then that "Ghost Parent" will have two child subs - The currently existing Parent and the new Subsidiary you have created. For your purposes, it sounds like you'll never need to report at the Consolidated "Parent" level, but it will exist for you nonetheless. You'll just have the two separate child entities operating side by side, rolling up to the Ghost parent (you can call it whatever you want) that never gets used and exists only because NetSuite allows only one top level subsidiary.