Just a couple of pointers:
1) Lay some ground rules. No Watch Tower publications may be used as proof. Watch Tower publications refernce other writings. Tell him to use those writings.
2) Show him that the whole concept of 1914 came from William Miller whom Charles Russell followed and believed. http://en.wikipedia.org/wiki/William_Miller_(preacher)
3) Show him that Charles Taze Russell, a Freemason, got the 1914 date from his measurements of the Great Pyramid of Egypt. http://en.wikipedia.org/wiki/Charles_Taze_Russell