Y offset for the game

Hi, I'm looking at addapting my game project to work in AR.  Unfortunately the phone's position at startup defines where 0,0,0 is.  When loading in a stage it would end up being centered on the person's head.  I'm wondering how it might be possible to set the stage at any position in the scene and then take the y offset of that position and apply that to the game logic?  Any thoughts or help on that anybody?