Hi John,
This is a bit outfield. But could you physically swap the drives so that D is C and alter the BIOS accordingly? I don't know how to read your system details, like I used to be able to, so I don't know if you're using SETA drives, although I suspect you are. You can then use your Windows disk to treat D: as a slave disk without losing your existing data. Did you say how you were using the RAID, ie what level, as my answer may conflict with that unless you can reconfigure the controlling application.
I've been out of combat for a while, so listen to the veterens first, before me. Good luck.