Can non-domain-connected users use Report Builder

I'm dealing with a scenario where SSRS is being provided to remote clients on a different domain. We've discovered that they can launch Report Builder (a ClickOnce application) from their Report Manager browser session, but RB then uses their local credentials when trying to do anything (e.g. hit a datasource) in the RB session. This article (http://technet.microsoft.com/en-us/library/ms365173(v=sql.105).aspx) seems to indicate that it won't be possible to hack our way around this; whereas this one about Azure (http://msdn.microsoft.com/en-us/library/windowsazure/dn189155.aspx) appears to indicate that a local RB session may be able to interact successfully with Azure - does this suggest there's a glimmer of hope? We are currently running SQL 2008 R2.