Actually the rule reads:
 
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Interference by spectators
SECTION 25  In the event that objects that interfere with the progress
of the game (my note: are there any other kind? ;-) )are thrown on the ice,
the official shall blow the whistle and stop the play; and the puck shall be
faced off at the spot where play was stopped.
 
Note 3:  If fans throw objects on the ice after being warned, a bench minor
penalty may be assessed against the OFFENDING FANS' TEAM for delay of game.
At the descrition of the referee, a warning may be issued before the game.
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So according to the rule, if you go to an away game and try this they could give
the penalty to the away team.  How they would determine who threw what would
be a different story.