HAOS on x86 - can't mount a 2nd HDD

Hi. I’ve just installed HAos from an image to the SSD of an old nettop PC. It runs smoothly without issues.

The machine has a 2nd drive, a slow but large HDD. I would like to have it mounted and accessible to use it for storing security footage from a MotionEye add-on. Since this HDD is slow compared to an SSD, I DON’T want to move all the HA stuff to it using the built in feature.

But since I can’t edit /etc/fstab on a read-only filesystem, I can’t do it.

What is a proper way to have a storage volume mounted and accessible by add-ons?