The actual configuration of which files to share is done by the script /usr/sbin/osso-usb-mass-storage-enable.sh, which is called from ke_recv binary with a parameter that tells it what to share.

You can easily change this script to actually share /dev/mmcblk0 when the parameter is /dev/mmcblk0p1, so it will share the whole device.

Note that this won't work if you use the other partitions, which you actually do unless you made some serious changes to your system.