> best non-back-end solution ... It's probably best to fix these before they even get to the browser.

Sure. But if you want to do this before "they even get to the browser", it's not going to be a "non-back-end solution". Anything that happens before your content gets to the browser is back-end by definition.

If you control the blogging software and/or the template, it would be trivial to replace the last space with   when rendering the page. Good ol' string manipulation, maybe a regexp or two. No need for JavaScript. I wouldn't be surprised if somebody already wrote a WordPress plugin to do this.