How to implement rel=author on a page with multiple authors?

I used the instructions on the article How To Implement Rel=Author for creating my page. The only difference is that I had two rel=author links instead of one. I then tested the page with Google's rich snippets testing tool, and the first author that was linked was displayed as if it were the only author. The second author was not displayed at all.

Multiple rel=author links is something that I think Google should recognize, as pages like forums and wikis usually have more than one author.

I couldn't find any author-specific information, but the HTML specs do allow you to define more than one link with the same relationship, e.g.

<link rel="alternate" hreflang="de" href="//de.example.com/my/page.htm">
<link rel="alternate" hreflang="en-gb" href="//uk.example.com/my/page.htm">
<link rel="alternate" type="application/rss+xml" href="/my/page.rss">
<link rel="alternate" type="application/atom+xml" href="/my/page.xml">
<link rel="alternate" type="application/pdf" href="/my/page.pdf">
<link rel="alternate" type="application/pdf" media="print" href="/my/print-page.pdf">
<link rel="alternate" media="handheld" href="/my/mobile/page.htm">

I would assume that the same could be done with the author relationship.

According to the HTML5 Working Draft:

The author keyword may be used with link, a, and area elements. This keyword creates a hyperlink.

For a and area elements, the author keyword indicates that the referenced document provides further information about the author of the nearest article element ancestor of the element defining the hyperlink, if there is one, or of the page as a whole, otherwise.

While the specification does not indicate a resolution for multiple authors specified at the HTML5 document level, the element level does provide support for multiple authors within a single HTML5 document (which should cover your forum's needs).