Adding bootable partition will make no use for you. All loaders reside in MBR first of all (at least all I know) and any attempt to modify the loader will erase previous loader like GRUB, Boot Manager etc.
So the resume is - either install Linux on second HDD (change the HDD priority prior to installing Linux) and then configure Bootable Recovery Capsule on another HDD. I've done this configuration on my home PC and 4 OSes + Linux Ubuntu 9.04 on two WD SATA 300GB drives. Then only inconvenience is to change drive priority via BIOS.