You can embed \x1b (escape) into a webpage. When you copy-and-paste that, it has the same effect as hitting ESC in the editor. So, I'd just have to make you copy "<evil command>#\x1b:wq\n" to also catch the case that you're using vim instead of directly pasting. However, I can't figure out a way to escape from nano.
(Tested it with the combination chromium+xterm+vim.)
(Tested it with the combination chromium+xterm+vim.)