Boot an Iso image
You can boot install a bootmanager on CD. That`s called ISOLINUX.
An even better method can be done with grub4dos. Grub4dos can act as an CD-ROM emulator. This is also possible if the BIOS has no native support for booting from CD-ROM.
Note: just like floppy emulation (MEMDISK or grub4dos) this will only work as long the operating system is accessing the virtual disk using the BIOS. After the operating system loads its own drivers for accessing the controller it's very likely that this virtual disk can be no longer accessed.
For examples, restrictions and workaround for booting ISO and floppy images with MEMDISK, see MEMDISK#ISO_images and MEMDISK#INT_13h_access:_Not_all_images_will_boot_completely.21.