Observing controller property (participating in queryparam) from service without observer

I moved state properties from controller to service except queryParams. now I would like to have one of the query param property to service.
Is there any way to achieve this without using observer ?.

controllers/application.js

import Ember from 'ember';
const {computed,observer} = Ember;
export default Ember.Controller.extend({
  myService:Ember.inject.service(),
  appName: 'Ember Twiddle',
  changedAppName:observer('appName',function(){
    this.get('myService').changeAppName(this.get('appName'));
  }),
  actions:{
    changeApp(){
      this.set('appName','NewEmberApp');
    }
  }
});

templates/application.hbs

<h1>Welcome to </h1>
<br>
<button >Change</button>
<br>

<br>
<br>

services/my-service.js

import Ember from 'ember';

export default Ember.Service.extend({
  appName:'SSS',
  changeAppName(param){
    this.set('appName',param);
  }
});

EmberTwiddle