this is done for the next 2.1 update which i will post later today.
To implement just put which track the album cover is for in the id attribute
<element type="AlbumCover" id="Tracks[1]" x="0" y="53" width="80" height="80" brightness="1.0" ></element>
<element type="AlbumCover" id="Tracks[2]" x="0" y="143" width="80" height="80" brightness="1.0" ></element>
one thing to keep in mind is if you positioning elements relative to the main AlbumCover and using the default skin, you should name the main album cover element to avoid naming conflicts
<element name="#AlbumCover" type="AlbumCover" ...
and reference #AlbumCover for the fields that are positioned relative to the album cover
<element type="Field" id="Artist" xAnchor="#AlbumCover.Right" x="30" ...