Was just looking for what this is before you posted.
cat'ing the language files shows that Mass storage mode and PC Suite are in hildon-status-bar-usb, which as far as I know is closed source.

e: as for the actual buttons, they're scripts, in /usr/sbin as I mentioned above.
pcsuite-enable.sh for PC suite mode
osso-usb-mass-storage-enable.sh for Mass storage mode.
Same for disabling them (unplugging), just replace enable with disable.

If you're thinking about executing pcsuite-enable.sh to trick it into host mode it won't work, you have to connect it to a real host till the driver is fixed.