Grid Control just give a nice interface to rconfig, so they are actually the same method as far as the conversion itself goes:http://docs.oracle.com/cd/E11882_01/rac ... m#BABEFFGE
The real details are presented in the os-specific install guides, for example:http://docs.oracle.com/cd/E11882_01/ins ... m#BABBAHCH
As for the manual process, I have never tried it so I would not know. I guess you could do a backup of the single instance and restore it to a single node of a cluster. Set the relevant cluster parameters and create the cluster views. Then fire up the other instances. Like I said, not done it, so just a guess. Personally I would go the rconfig route.