No, there is no migration path from a already working, bootable OS volume on a hard drive, to add a drive and magically turn it into a working RAID array bootable volume.
Creating a RAID volume, you see, formats all drives in the volume.
you CAN however, add *2* drives, create a RAID0 volume, install the RAID array drivers on your OS, then use Ghost or Acronis "image" the Os onto the newly created RAID volume, then disconnect the original OS drive and try to boot to the RAID volume.
Complicated and time consuming, and leaves you with a drive at the end.
Rapebear Attacks! RAWR!