A little workaround I thought of (instead of using an external editor) is to replace with a substitution of a template that outputs a newline. I don't know of such a template on any wiki (for example, Template:Break on enwiki evaluates to <br />), so I put <onlyinclude></onlyinclude> surrounding a newline on my user page and now use {{subst:user:wqnvlz}}.