Save associated Model data before Form submission - cakephp

Question

I have a polymorphic attachment model between Article and Image (alias for Attachment model) ala https://github.com/josegonzalez/upload. Article hasMany Image. Image is an Attachment.
When the form is submitted via the Article form's save button, everything saves properly, including associated models.
However, I have set up a dynamic display of attached images so that the user can choose which one to use for the article's preview before saving the article. The dynamic image display works (proved by deleting row in phpMyAdmin), but I cannot figure out how to upload and save the associated Image that has been selected without pressing the submit button. I'd like to upload the image immediately upon selection (or upon a button press that does not submit the article, too!
Here is the relevant form section, and the script that eventually results in the display of all associated Images.
<div id='imagesControl'>
<?php
//TODO gotta make this happen live
echo $this->Form->input('Image.0.attachment', array('type' => 'file', 'label' => 'Image'));
echo $this->Form->input('Image.0.model', array('type' => 'hidden', 'value' => 'Content'));
echo $this->Form->input('Image.0.foreign_key', array('type' => 'hidden', 'value' => $id));
echo $this->Form->input('Image.0.id', array('type' => 'hidden')); //Thought this would help
?>
<div id='attachedImages'>
</div> </div>
<script>
$(document).ready(function() {
$('#imagesControl').change(function() {window.alert("sometext");
$("#attachedImages").load('../imageDisplay/<?php echo $id ?> #attachedImages',
{id: $(this).attr('id')});
})
.change();
});
</script>
Notably, in the view file '../imageDisplay' that gets rendered, $this->data only contains the div id sent via $(this).attr('id'). I cannot find a variable, anywhere, that contains the file I chose in the input section before the form saves (the file I'm trying to upload and save). It's apparently there, because it does save using $this->Article->saveAll() automagic.
However, I cannot even begin to guess where / when / how I can upload the image and add a row to the attachments table containing the new image's data without submitting the article. I've been stuck for days.