Responsive Images - Generating multiple images from Theme Customizer control upload?

Question

So, after poking around in the code it looks like the filter image_make_intermediate_size is not called by the various WP_Customize_Control() classes at either WP_Customize_Image_Control() or it's parent WP_Customize_Upload_Control().

I'm looking to auto-generate images of various sizes, for responsive image serving and I need to execute the image_make_intermediate_size() function with some custom sizes that are specific to my extended custom control. Just not sure how to ensure that the uploaded images call this function mainly because I haven't been able to track down where or how the upload functionality of WP_Customize_Control() is "unhooked" from the default upload behavior where the function is normally executed.

Note that the way it works is obviously the best option, don't want every image uploaded through the theme customizer to auto-generate all the default image sizes, but for my use case, I prefer to use native functionality and just pass some unique size paramters to image_make_intermediate_size().