A nice way could be:
Make a theme made of xlabellight.(just one module)
in there make labels that represent your themes.
you can make it look pretty good having all the screen to doit.
on the click action for each label: ["$LiteStepDir$utilities\LSThemeInstaller.exe" /switch Anytheme]
and also make a shutdown label.
then on all your themes make a shutdown label to this welcome theme.and shutdown from the welcome theme so next time the pc start it starts from there.
just an idea.