Assassin's Creed II - Last Rites - How to bypass the guards

During Sequence 13 of Assassin’s Creed II, ‘Bonfire of the Vanities‘, I need to kill Savonarola’s lieutenants, one of which is the chanting monk at the top of the dome of the Basilica di Santa Maria del Fiore, in Memory 5, ‘Last Rites‘:

Climb the Duomo without being seen and remove the entranced priest from his perch.

There are many guards. I can see the part of the dome where I need to be, but I am not able to get there without being discovered or falling.
Does anyone have any strategies or advice?