Are there any themes that dont use number of products per row? Instead do it kind of like the images on pinterest - just add as many as fit (without floating them I guess
Or can you modify the front view for instance?
You can modify the layout to virtually anything you want, assuming you have sufficient basic HTML, PHP and css knowledge. Use template overrides for your modified template files.
Some references:
http://forum.virtuemart.net/index.php?topic=90935.0
http://forum.virtuemart.net/index.php?topic=98505.0
http://dev.virtuemart.net/projects/virtuemart/wiki/Hints_for_the_use_of_the_template_system
http://www.ostraining.com/blog/joomla/overrides