This is a hardware question specific to your BIOS and RAID controller implementation?
Or are you attempting to do this with a software RAID implementation?
Regardless, it does not sound advisable, to me. What is the holdup on getting the second disk? Can't you just wait to have a stable disk array?
Alternately, you could install the OS to the single disk without RAID, backup the install, and migrate it once you get your second disk.