Lightbox and TinyMCE for multiple images?

[jpa]

I found the topic Simple way of opening images to Lightbox window with TinyMCE
This solution works perfect for one single image added by a user via TinyMCE.

But how can I make use of the prev/next function when the rel=lightbox is added via the TinyMCE link window?

In my non-CMS private web page I use the code rel=lightbox[groupname] to allow for quick navigation between these images.
But I can't find out how to implement this in the TinyMCE link window.

And even if I add the [groupname] in the html code myself, it does not work at all. It still says "Image 1 of 1" and no prev or next buttons when I preview one of the images on the page.

How can I make this work? Is it even possible?