Fair enough, the only thing I can think of that may help is to use Texture Atlases, at least if you aren’t using them already or haven’t considered them. From the wikipedia page:
In web development, images are packed into a sprite sheet to reduce the number of image resources that need to be fetched in order to display a page.
Having said that I’m not sure of the details of your project, and how easy it will be to implement something like this.