a script in the bootable partitions startup-sequence could remap the system assigns to another drive and hand off to its startup-sequence, though that can be a pain to set up. At least you wouldn't have to actually set another drive as a boot device.
thats what I used to do - a key detector (amiga, ctrl, shift..) that branched into multiple sections of the startup-sequence. yes, a bit of setup, but very flexible
Tom UK
