This problem of multiple inputs has been discussed before. But there is a way to do it, at least for Windows, by embedding images in the plugin itself.
I have just finished a plugin generator that embeds the shader and images in the plugin. So you can save an effect plugin, for example, that has images other than that supplied by the host. In particular this is useful for shaders that depend on a noise image. You can save up to four images and three of those can be saved with an effect.
Here's the announcement about it.
http://spout.zeal.co/forums/topic/shade ... er-update/
I also set up a template for programmers to use ( https://github.com/leadedge/FreeframeMaker
). It's more general purpose than the original ShaderMaker project and does require a bit more work as a result. But it's not limited to the ShaderToy specification and I hope it works for the various ideas that people have and you can get some use out of it.
Cheers to all.