I found this: ASP.NET forms authentication - auto login with a test account while debugging? - which would get me half the way there.
What would be the recommended approach to attach roles to the signed on user (for testing different permissions). I have a custom membership / role providers - so I guess I could override the role providers while in testing / debugging mode to grab a test role out of webconfig app settings etc. - but I don't want to be over thinking it where there may be a simple solution.