Unable to bring custom image maps into multiplayer via a saved toolbar

Question

I recently had the idea to use a tool to make an image into a map, then bring them into a multiplayer server via a saved toolbar. Problem is, the maps are reset whenever I load the saved toolbar on a server, or even on another saved game.

Someone else here from 2 years ago wanted to do a similar thing, but couldn't figure out how. He got an answer, but it was the method I tried that doesn't seem to work anymore. Plus, I don't have enough reputation to comment on the answer to say that it doesn't work.

Are there any other ways (outside of having access to the inner workings of the server), or is it forever impossible?