just_an_idea.js

var application = Sammy.Bundle('#element', 
    {
        'base': my_app.base, // A Sammy.Application in its own right
        'add-event': my_app.add_event // So is this
    }, 

    function() {
        // Rules how to change states. Can be triggered by binding or routing?
        this.get('#/add', function() {
            this.setApplication('add-event');
        });

        this.bind('some-event', function() {
            this.setApplication('base');
        });
    }
);

$(function() {
    application.run();
});