This isn't doable through Excel, that can only handle one image per product. With WSI, just check out the Master Doc Reference, it shows how to do this:
Code:
<Images>
<Icon Extension="gif|jpg|png|jpeg" Delete="boolean">base64 encoded image data here</Icon>
<Medium Extension="gif|jpg|png|jpeg" Delete="boolean">base64 encoded image data here</Medium>
<Large Extension="gif|jpg|png|jpeg" Delete="boolean">base64 encoded image data here</Large>
<ImageFilenameOverride/>
−
<MultiImage>
−
<!--
use index can be 1 to 10, and use blank color for "no color" image
-->
−
<Icon>
<Img Index="1" Color="" Extension="gif|jpg|png|jpeg" Delete="boolean">base64 encoded image data here</Img>
<Img Index="1" Color="" Extension="gif|jpg|png|jpeg" Delete="boolean">base64 encoded image data here</Img>
<Img Index="1" Color="" Extension="gif|jpg|png|jpeg" Delete="boolean">base64 encoded image data here</Img>
<Img Index="1" Color="" Extension="gif|jpg|png|jpeg" Delete="boolean">base64 encoded image data here</Img>
<Img Index="2" Color="" Extension="gif|jpg|png|jpeg" Delete="boolean">base64 encoded image data here</Img>
<Img Index="2" Color="" Extension="gif|jpg|png|jpeg" Delete="boolean">base64 encoded image data here</Img>
<Img Index="2" Color="" Extension="gif|jpg|png|jpeg" Delete="boolean">base64 encoded image data here</Img>
<Img Index="2" Color="" Extension="gif|jpg|png|jpeg" Delete="boolean">base64 encoded image data here</Img>
<Img Index="3" Color="" Extension="gif|jpg|png|jpeg" Delete="boolean">base64 encoded image data here</Img>
</Icon>
−
<Medium>
<Img Index="1" Color="" Extension="gif|jpg|png|jpeg" Delete="boolean">base64 encoded image data here</Img>
<Img Index="1" Color="" Extension="gif|jpg|png|jpeg" Delete="boolean">base64 encoded image data here</Img>
<Img Index="1" Color="" Extension="gif|jpg|png|jpeg" Delete="boolean">base64 encoded image data here</Img>
<Img Index="1" Color="" Extension="gif|jpg|png|jpeg" Delete="boolean">base64 encoded image data here</Img>
<Img Index="2" Color="" Extension="gif|jpg|png|jpeg" Delete="boolean">base64 encoded image data here</Img>
<Img Index="2" Color="" Extension="gif|jpg|png|jpeg" Delete="boolean">base64 encoded image data here</Img>
<Img Index="2" Color="" Extension="gif|jpg|png|jpeg" Delete="boolean">base64 encoded image data here</Img>
<Img Index="2" Color="" Extension="gif|jpg|png|jpeg" Delete="boolean">base64 encoded image data here</Img>
<Img Index="3" Color="" Extension="gif|jpg|png|jpeg" Delete="boolean">base64 encoded image data here</Img>
</Medium>
−
<Large>
<Img Index="1" Color="" Extension="gif|jpg|png|jpeg" Delete="boolean">base64 encoded image data here</Img>
<Img Index="1" Color="" Extension="gif|jpg|png|jpeg" Delete="boolean">base64 encoded image data here</Img>
<Img Index="1" Color="" Extension="gif|jpg|png|jpeg" Delete="boolean">base64 encoded image data here</Img>
<Img Index="1" Color="" Extension="gif|jpg|png|jpeg" Delete="boolean">base64 encoded image data here</Img>
<Img Index="2" Color="" Extension="gif|jpg|png|jpeg" Delete="boolean">base64 encoded image data here</Img>
<Img Index="2" Color="" Extension="gif|jpg|png|jpeg" Delete="boolean">base64 encoded image data here</Img>
<Img Index="2" Color="" Extension="gif|jpg|png|jpeg" Delete="boolean">base64 encoded image data here</Img>
<Img Index="2" Color="" Extension="gif|jpg|png|jpeg" Delete="boolean">base64 encoded image data here</Img>
<Img Index="3" Color="" Extension="gif|jpg|png|jpeg" Delete="boolean">base64 encoded image data here</Img>
</Large>
</MultiImage>
</Images>