I'm sure you could use a laser style sight that way he could hold the gun and all while you help position it on the deer. Thi way you are not trying to look around him and not getting in eachothers way. Some states have laws against using these but 'm sure there are ways around it ke in your situation.
Brandon

Something like this.
http://cgi.ebay.com/FULL-SET-LASER-POINTER-SIGHT-SCOPE-FOR-GUN-PISTOL-RIFLE_W0QQitemZ320050241950QQihZ011QQcategoryZ6682 7QQrdZ1QQcmdZViewItem