I made a little plugin that loads some javascript that detects ad blockers and puts up a nag box at the top of the page.
It can be found at: Beta test Plugins.
I did not make it configurable, so you have to manually edit the message if you don’t like the stupid one that I put there.
One nice thing is that you can grab just the javascript file after you download the plugin and unzip it, and use it on any page, even ones that are not WordPress pages.
Ad Blockers are continually adding to their filters to prevent this kind of script, but for now it works with uBlock, and that’s pretty good.