The bloogle theme is a demo, so its not necessarily complete, but most of it is there. Unfortunately I haven't been able to spend as much time as I'd like, but you are welcome to it. You can download it from SourceFourJs at
http://code.google.com/p/sourcefourjs/downloads/list.
As to selecting multiple themes, this is simply just a combobox in the html page that executes a javascript function when the value changes. The JS function sets a variable that alters the URL to launch the GWC application.
Eg. if you have an app config to start an application called foo, you could have a config for each style:
foo-genero.xcf and foo-bloogle.xcf
and so the URL could be http://.../wa/r/group/foo-genero or http://.../w/r/group/foo-bloogle
HIH & regards,
///M