I don't think what you're asking can be done with the standard Windows system.
The best solution IMO is a second hard drive and a removeable caddy. This fits into a 5¼" bay and takes standard hard drives. That way you have total peace of mind, independent use of the same PC, nobody can blame anyone else, and you have a backup you can store safely away from the PC to protect against theft, etc.
A pair of drive caddies will cost less than £20 and a new drive will give you additional storage and greater speed too no doubt.