Rule 22
Requiring Opponent or Fellow-Competitor to Leave Ball to Assist Play
Q. Is it permissible to request an opponent or fellow-competitor to leave his ball close to the hole in case it will assist my play?
A. There is nothing in the Rules that prohibits a player from making such a request. However, if the opponent or fellow-competitor feels the ball may assist your play, he does have the right to lift his ball, and may not be denied this right.
http://www.usga.org/questions/faqs/r....asp?FAQidx=89