You can install it the same way like on sd-card. All you need is a emmc-adapter for your card reader/writer. With the adapter the emmc-card apperas to be a sd-card.
If you can not find an adapter try the following. Install the image on a sd-card. Start the device from the sd-card but with attached (empty) emmc. Copy (i.e. using ssh, scp, rsync) the image (*.img) you want to install as a file onto the sd-card. Then sudo dd if="/path/name.of.the.image.img" of= /dev/mmcblkX bs=1M. Wait long enough. sync. Switch of device and remove sd-card.
I wish you luck.