Blogging this mainly for my benefit, but if anyone else finds it useful - you're welcome :) In case you're working on a SharePoint site where the branding requires the removal of the Welcome links control then you'll loose the ability to 'Sign in as a Different User' to check the look-and-feel and functionality that different users will experience. One possible solution is to adjust you browser settings to always prompt for credentials and then restart your browser every time you need to sign in...
Download it from here! sweet