Theoretically yes its possible.
Practically, it'll probably take forever. I'd just reinstall everything.
Think about it - you'd have to basically write 1/2 of your drive to the 2nd HDD, then shift all the contents on teh 1st drive to match the 2nd HDD's RAID 0 configuration. 1) thats scary... 2) the possibilities of a screw up is reallllllly high. One sector off and its screwed up both drives and a reinstall is waiting to happen anyways.
Besides, life'll probably be alot faster and better w/ a complete reinstall. Free raptor? I'd reinstall everything for a 2nd raptor!
Also I don't know if you're going to see any performance w/ a RAID 0+1, so it might not be worth the reformat.