I guess it depends on what kind of users do you wish use: AD or VSM local.
1. For AD users I think the only option is to start the browser application specifying different AD user credentials (e.g. <Shift>+<mouse right click on IE icon> -> Run as different user.).
2. For VSM local users (w/o domain information) you may try creating another VSM system (referring to the same database) and web virtual directory using anonymous access. Please check the document "API User Guide" for Authentication advice (you will find not so much info though). Do not use NOAUTH attribute in that case - as I know it's just for admin account.