Overriding Parent Theme Image Sizes w/o Rewriting Template Files

My sites current theme creates way too many unused image sizes, and I was about to integrate this plugin into out site by way of a child theme. I thought I would be able to just remove the parent themes add_image_size() calls and replace them with fly_add_image_size(). However I didn’t realize that the dynamically generated image sizes needed to be called by the plugin functions within the templates themselves.

Am I missing something? Is there some way to dynamically generate the themes thumbnails without changing every unique call for get_image_size() within the theme?