I think DualBoot is the primary feature of this magic piece of software. I would ask if it's possible to join the link to the external SD card so both ICS and JB can use it succesfully without to change path in every app where it's required.
Its build in:
Settings - purr Nexus settings - navbar - last entry navbar customization
But if you reboot it's invisible but still active until you do a system UI restart. It's a known bug....4169234
Ah.. this is a true missed one for me.. What ...