hook the tail end of the halyard to the Shamrock and let someone else pull you up the mast using the other boat.
Actually, first off make sure your bosun chair isn't one of the ones that has been recalled by Taylor made. If you want to help "pull" yourself up the mast with your hands, use another halyard to pull up a thicker strand of 3-strand and pretend you are in gym class again. You can also use three Prusik Knots and climb the halyard itself. Put the bosun's chair tied onto one, and then tie two more, one for each foot. Climb up the halyard by alternating pressure on each knot and moving the loose one up the halyard.
The Prusik Knot or Triple Sliding Hitch