WordPress 3.5 Media Manager: Is there a "good" way to add an additional select option within Create Gallery tab?
Most of those select-dropdowns are from wp-includes/media-template.php, which has a lot of Underscore templating (<script type="text/html" tags), but few action hooks for php code. With Javascript you can bind the Backbone.js hooks for wp.media events, such as wp.media's open/close events. From such event you could grab that Images/uploaded-to-page selectbox with jQuery('.media-modal-content:visible .attachment-filters'), add item(s) and listeners as needed. I'm pretty sure there should be a much better Backbone.js-style solution, though.
Here is a tutorial by Shiba Shake on this subject ...
How to Expand the WordPress Media Manager Interface
Hope this is helpful to you!