Creating rootfs_data mount?

My device keeps the created ELF-bin in RAM, and has nearly a Gb of Free space allocated for this particular image (/dev/mmcblk1p3, in this case). I would like to use this partition as the rootfs_data so I can keep the packages there.

One thing to keep in mind is that currently I am pivot'ing exec switch_root, so I would need to do any moving of the initial rootfs_data, or whatever it is called for, through command line.

Here is my /etc/config/fstab

config global
        option anon_swap '0'
        option anon_mount '0'
        option auto_swap '1'
        option auto_mount '1'
        option delay_root '5'
        option check_fs '0'

config mount
        option target '/mnt/mmcblk1p1'
        option uuid '0043-53BE'
        option enabled '0'

config mount
        option target '/'
        option uuid 'b40188e3-4cae-43be-a339-6e2d0b4a8c92'
        option enabled '0'

config mount
        option target '/mnt/mmcblk1p3'
        option uuid '65e8b550-2a1a-4882-b290-6d3081eda2a8'
        option enabled '0'

config mount
        option target '/mnt/mmcblk1p4'
        option uuid '483fc6fb-3825-4b0f-97b8-810d65f5146d'
        option enabled '0'

config mount 'overlay'
        option uuid '65e8b550-2a1a-4882-b290-6d3081eda2a8'
        option target '/overlay'