To create a multiple column layout of the In-line Multi you would need to modify the inlinemulti.html file of the Amazon Theme Template Set you are using.
It would be a good idea to make a copy of the Amazon Theme Template Set you are using like suggested on the this video at about 4:28. http://www.wpzonbuilder.com/blog/how-to-modify-a-wordpress-template/
Or you can attempt to modify the Theme Template Set your are using now by going to:
Replacing the /default/ with the Theme Template Set you are using as shown on the “WPZonBuilder General Settings” -> “Template” page in the “Template Set” drop down box. Once you have the URL set up correctly you can copy and paste it into your browser and hit enter. You will be brought to a page where you can edit the HTML code right in WordPress and not have to use FTP.
Copy and paste the code below into the edit box replacing the existing code and click the Update File button. Create a post with an In-line Mutli to see how the results will display within your theme’s layout.
The CSS code below my need some adjustments to work within your theme’s layout. The 2 to watch are the width and height. Those setting should get you close to a 3 column layout with a uniform height. If you want a 2 column layout you can change the width to somewhere around 44% and the height would need to be adjusted or removed. You will see that adjusting the width to a smaller percentage can give you more columns if needed.
border: 1px solid #CCC;
<a [relnofollow] [targetblank] href="[DetailPageURL]" class='amzn_multititle'>[Title]</a><br /><br />
<a [relnofollow] [targetblank] title="[Title]" href="[DetailPageURL]"><img alt="[Title]" src="[SmallImage]" /></a><br />
<span class='amzn_ratingtext'>Average Rating:</span> <span class='amzn_rating'><img src='[StarURL]' style='border:none;' /></span><br />
[TotalReviews] total <a [relnofollow] [targetblank] href="[DetailPageURL]">customer reviews...</a><br />