after a little thinking....i have something to share.....i was trying something called the five tibetan rites a few years ago....and i think this is useful for manipulating the c1.....i remember i could follow the openeing of different meridianes...and one was going up thru the skull of the backhead...every time i started to do this yoga things started to happen in this meridiane line....beside from this my jaw started to crack beside my very upper part of the neck and the column....i would mabye locate it to the c1 or c2......this yoga is also very good for opening up the chest and the solar plexus...
here is a link:
http://www.mkprojects.com/pf_TibetanRites.htm