I'm about to issue these instructions would appreciate it if you could quickly confirm covers your advice correctly and nothing missing:
1) Setup a completely different GWT account unrelated to the main site, so that there is a new GWT account specific to the staging subdomain
2) Add a robots.txt on the staging area subdomain site that disallows all pages and all crawlers OR use the noindex meta tag on all pages. Its obviously very important when you update the main site it DOES NOTinclude or push out these files too (since that would result in main site or pages being de-indexed)3) Request removal of all pages in GWT. Leave the form blank for the page to be removed since this will remove the entire site4) After about 1 month (or you see that the pages are all out of the serps), and google has spidered and seen the robots.txt, then put up a password on the entire staging site.Note:For brand new sites staging areas that don't yet exist or exist but are new and not yet showing up in the index then simply add a password for human access to prevent the above process being required in the future.