I have a helper like
Template.user_profile.helpers({ user:function() { return Meteor.users.find({\'profile.front_name\':Session.get(\'slug\')}).fetch(
I've just accidentally discovered this in the console:
Template.registerHelper function (name, func) { Blaze._globalHelpers[name] = func; }
So, Blaze._globalHelpers is what we are looking for!
Blaze._globalHelpers