Observing itemController

Good day.

I know that there is @this @this source, that can be used to observe itemController properties.

How can I use @this or something similar to observe itemController properties in such case:

Template:

{{#each headers itemController='headerItem'}}
    {{! skip}}
{{/each}}

ArrayController:

headersPropertyChanged: function() {

}.observes('headers.@this.property'), // what should I use?

ArrayController has another itemController for main model.

Thanks.