It seems is not possible. I need to setup some public workstation in my library where many people can turn on.
I wrote to meraki support and they said meraki does not provide a way to logoff the user excluding forcing the logoff from administrator dashboard. That's crazy, I think.
I use my radius server authentication methond passing trough the meraki splash screen.
I tried to change the workstation mac address but seems does not works and for the splash screen timeout time there's no way to use the workstation with different user. When the first user login the couple user/device rest logged.