Session.set() upon route event in Meteor

I have this functionality associated with clicking a button:

 'click .single-speaker-info a': function(ev, speaker){
    ev.preventDefault();
    Session.set('selectedDocId', this._id);
}

But I'd like it to happen upon hitting this route

Router.route('speaker', {
        path:'/speakers/:_id',
        template: 'speaker',
        data: function(){
            return Speakers.findOne(this.params._id);
        },

        //my attempted solution
        selectedDocId: function(){
            Session.set('selectedDocId', this._id);
        }
    });

But I can't find any documentation on how to execute a method on a route.

Here is the Template.helper Im using to get the property Im setting

       Template.speaker.helpers({

            editingDoc: function(){
                return Speakers.findOne({_id: Session.get('selectedDocId')});
            }

        });