I've looked through the controller source code and it doesn't look like there is a built-in way to access the controller from the element (https://github.com/spine/spine/blob/dev/src/spine.coffee#L482). What I do is make a global variable to hold the controller so that I can access it from other places:
app = new App()
# inside of App constructor:
@foo_widget = new App.FooWidgetController()
# from other non-spine code:
app.foo_widget.method()
Another option would be to do the association yourself using jquery's data() method:
class App.FooWidgetController
constructor: ->
super
@el.data 'controller', this
# from other code:
$('#widget').data('controller').method()