I haven't checked in S805, but the S9xxx possible to install the system with the core 4.xx on eMMC in normal Linux partition mode. If you are using kernel 4.x, you can try the same option on s805. To use kernel 3.10, you need Android partitions of the correct size.Alternatively, you can try to change the installation script so that it places part of the data in different partitions (/dev/system and /dev/cache), preformatting them in ext4. and add new options to fstab to mount these partitions to new points
