how can I remove observers from a property assigned to an ember computed alias?

if you have a property assigned to an Ember.computed.alias (or Ember.computed.oneWay), how can you remove its observers dynamically?

additional context:

i have a computed property that i'm passing to a component: time=activeSongProgress. activeSongProgress updates about every 100ms or so. I'd like to be able to assign it to a property on my component as a computed alias:

export default Ember.Component.extend({
    ...
    value: Ember.computed.alias('time'),
    ...
});

and then be able to dynamically unbind value, set it to something else, then assign it back to the computed alias.

e.g. Ember.defineProperty(this, 'value', Ember.computed.alias('time'));)

when i'm dragging the mouse, i don't want value being set by an observer every 100ms, so i need a way to unbind value from time. currently i'm getting the behaviour i want by adding and removing observers:

// app/components/progress-bar.js
import Ember from 'ember';
export default Ember.Component.extend({
  tagName: 'input',
  attributeBindings: ['value', 'type'],
  type: "range",
  value: 0,

  setValueAsTime: function() {
    this.set('value', this.get('time'));
  },

  setTimeObserver: function() {
    this.addObserver('time', this, 'setValueAsTime');
  }.on('init'),

  mouseDown: function() {
    this.removeObserver('time', this, 'setValueAsTime');
  },

  mouseUp: function() {
    this.addObserver('time', this, 'setValueAsTime');
  }
});


<!-- app/templates/songs.hbs: -->
{{progress-bar time=activeSongProgress}}

which works great, but i think i'd prefer to do this with computed aliases.