one of the issues of dual booting android with ubuntu touch is not being able to access your files in the other OS.
in ubuntu :
the android files (or /sdcard/ content) are located at /userdata/media/0 while your files are at ~/. make a mount point and bind these two directories: (i used adb for this)
$adb shell #su - phablet $cd ~ $sudo mkdir android $sudo mount --bind /userdata/media/0 ~/android $sudo chmod 775 android $sudo chown phablet:phablet android
in android :
ubuntu files are at /data/user-data/phablet/ while your files are at /data/media/0. unfortunately only the app that performs the mount (for me terminal emulator) can see the files i don't know why... more info @ http://forum.xda-developers.com/show....php?t=2065856
and as you can see stickmount doesn't support nexus 4. so if you've got something else give it a try
mount -o bind /data/user-data/phablet /data/media/0/ubuntu
i've got a nexus 4 but it should work for all supported devices.