OK, so on hook fetch_session_complete you'd do this:
PHP Code:
global $do_something;
$do_something = true;
Then in global_setup_complete:
PHP Code:
global $do_something;
if ($do_something)
{
// your other code here
}
Obviously you can choose whatever variable name you want in place of $do_something. Choose something that's unlikely to conflict with an existing global.