VueJS 2 - Listen to event in mixin - vuejs2

Question

I'm currently trying to create a mixin for Vue which basically creates a property passthrough chain. I'll clarify what should happen to be a little more clear;
Let's say I got 3 components; A,B and C.
A & B are both the same component called 'content-pane' (See below for template code).
<div class="pane-wrapper">
<div class="content-pane" :class="{'is-hidden' : !active}" :content="name">
<div class="card white">
<div class="card-title grey darken-3">
<h1 class="white-text">{{ label }}</h1>
</div>
<div class="card-content white">
<component
:is = "type"
:routes = "routes"
:passthrough = "passthrough"
keep-alive
></component>
</div>
</div>
</div>
<content-pane
v-for="(pane, key) in children"
:key = "key"
:label = "pane.label"
:name = "pane.name"
:active = "true"
:type = "pane.type"
:routes = "pane.routes"
></content-pane>
</div>
C is a dynamic component, meaning that it is interchangeable and could be any component.
Now I want to be able to access certain data from component C in component A, and for that I am trying to create a mixin that dyamically offers a data property to do this:
<script>
export default {
name: 'passthrough',
props: {
passthrough : {
type : Object
}
},
data ()
{
return {
// This object allows you to
// update the parent.
passthroughModifier : {
// We use the data object inside the
// original object because Vue doesn't
// want to detect direct prop changes
// when they are added dynamically
// into the root object...
data : {}
}
}
},
methods : {
/**
* This function fires an emit event.
*/
emitUpdate ()
{
this.$emit('passthrough-update', this.passthroughModifier);
}
},
watch : {
/**
* Emit an event once the passthrough
* property has been changed.
* We need to use a deep watcher.
*/
'passthroughModifier' : {
handler : function (val) {
this.emitUpdate();
},
deep: true
}
},
created ()
{
// Allow access to the instance
// inside the iteration.
let _that = this;
// Attach a listener for the passthrough update
// which will walk through all the keys in the
// data object and hard-set these locally.
this.$on('passthrough-update', function (data) {
Object.keys(data).forEach(function (index) {
_that.passthroughModifier[index] = data[index];
});
});
}
}
Everything works fine except listening to the 'passthrough-update' event, which is fired by the watcher on $.passthroughModifier.
So; When component C updates its $.passthroughModifier.data, the event gets emitted, but component B isn't able to catch this event.
I have tried to listen for this event in the created() method of the mixin (see code above), but it seems as if the event only gets caught in the component the event is fired from. So component C fires the event, and component C listens to its own event.
I hope someone is able to tell me wether this is actually possible or not, and what I'm doing wrong if it is possible.