Customizing the attachments login page

Does anyone know if there is a way to customize the HTML login page users are directed to when trying to open attachments of archived emails?  Right now when a user wants to view an attachment of an email that has already been archived into SourceOne they are directed to an HTML page to log in and it is the default out of the box text.  I want to add 1 line somewhere that gives them an example on how to login with domain and username, it does say this now login using domain\username format, but we have users who dont know what the domain is so I want to put it on this page so that they are aware.