I found my answer and I did not need to instantiate the injector myself to get the service.
Services are injectable in the run() function, so doing:
angularApp.run(intializeAngularApp);
with
initializeAngularApp($rootScope, $location)
{
$rootScope.location = $location;
$rootScope.$watch("location.url()", function () { alert("url changed"); });
}
works.