Hello,
I'm sorry, my mistake - you can't change this behaviour using VM configuration, it is hard coded and SEF support for this is marked as TODO in the code. If you are up to some code digging, the redirection functionality is located in /administrator/components/com_virtuemart/html/shop.browse.php file on line 82. You could also report your request to VirtueMart developers.
Best regards,
ARTIO Support Team