I could be wrong, but I don’t think that would work.
All of those techniques add style attributes to existing HTML elements, in the generated output. But, in the case of <var> the actual tag is stripped out of the generated HTML. So, there’s nothing to style.
I could add a span to style a bit of text with italics, sure… but I could just use MarkDown for that. It still wouldn’t be the same as wrapping the text in <var>…</var>. <var> is semantically different from merely italicizing text (even if it typically displays that way), particularly when it comes to devices that parse the actual page content, such as screen readers & other assistive technologies.
…Unless I’m misunderstanding the information from that post you linked to?