I have several comps with 'MSI' motherboards. On these I can press F-11 key for a one time setting of boot order (C:\ - D:\ - E:\ - etc - shows usb drive, list of attached hdds, make/model of cd/dvd drive - no actual drive letters) Off & on again, back to bios settings.
'DELETE' goes to bios, there I can set whichever/whatever location (usb - hdd - cdrom) to Always boot from.
Would this work for you? Or am I missing something?
-c-
edit: this works for me with XP-32, XP-64, ubuntu, Mint, etc. never tried same os on 2 diff hdds. <-whats the point?
I dont normally do this 'cause all drives are accessable by whichever os hdd I booted from.
I have three 'hot swappable' drive bays, I have [after booting] powered up same os hdd = maybe E or F or etc & copy/move files at sata speeds, or replace corrupted system files {the ones that dont ever get modified by os}