How can I add entries to grub/grub2 for booting off of removable media, like optical discs, as well drives that aren't supported by the bios for booting (but otherwise work fine in Linux), like super disks and zip drives
GRUB/GRUB2 uses the functions of system firmware (i.e. BIOS or UEFI) to do its job, so if the BIOS does not support a particular removable media device, you'd need to write a custom GRUB2 driver module that would implement all the necessary routines for accessing that device.
For optical discs, the first problem is that the BIOS may provide the interface for booting from them only when it is actually booting from them. There is no standard interface for programmatically telling the BIOS "I changed my mind; I want to boot from an optical disk after all, please activate optical disk support."