Remove attachment fields from custom media uploader

I’ve got a custom media uploader setup and trying to remove attachment fields from only this uploader, while leaving the fields intact for the default WP post/page media uploader. Everything works great except getting the fields to be excluded behaves oddly.

Here’s a bit of code on how it works:

First, open uploader thickbox with this js tb_show(box_title, 'media-upload.php?post_id=0&custom_uploader=1&TB_iframe=1' );

Next, add the custom_uploader value to the form action URL

function upload_request_hook( $form_action_url, $type ) {
    $form_action_url = $form_action_url . '&custom_uploader=1';

    return $form_action_url;
}

The iframe url for my custom uploader now looks like: media-upload.php?type=image&tab=type&post_id=0&custom_uploader=1 and the form action is something of the same. So it’s all good there.

For testing purposes, I’m removing all attachment fields

function image_attachment_settings( $form_fields, $post ) {
    unset( $form_fields );

    return $form_fields;
}

Then adding the filter and action:

function image_upload_options() {
    add_filter( 'media_upload_form_url', 'upload_request_hook', 10, 2 );
}

if ( isset( $_GET['custom_uploader'] ) || isset( $_POST['custom_uploader'] ) ) {
    add_action( 'admin_init', 'image_upload_options' );
}

So I’m trying to use the if ( isset( $_GET['custom_uploader'] ) || isset( $_POST['custom_uploader'] ) ) to only apply the filter/action for my custom uploader, based on the form action.

But here is the first odd bit. It works how I’m expecting if I use the HTML upload method. If I use the Flash uploader, none of the fields are removed.

And the second odd bit … If I remove the IF statement, where it basically removse the attachment fields for every upload type (custom and default WP), it works with both the flash and HTML uploader. But thats defeating the purpose.

The question here is; what can I setup here to exclude the attachment fields for only the custom uploader, where it works with the Flash and HTML uploader? Any type of IF statement to apply? Any other hooks I could setup or latch on to?

Appreciate any help that could be given here. Thanks!