For Mobile access, the top channel is changed to the WirelessDesktopDispatcher. With this channel, we can choose the first channel to display depending on the client capabilities.
So, if you find/develop something similar which choose the first channel to display depending on a parameter (the organisation) the user could specify, you define a different top channel for each organisation desktop, and when the parameter change, the desktop switch.
If you only want to switch desktops, you can give him links to the different desktops by adding "provider=YourContainer" to the portal url.
e.g.:
http://yourserver/portal/dt?provider=JSPTabContainer
http://yourserver/portal/dt?provider=JSPTableContainer
hth
Chris