Sort product listing by multiple columns?

-- HikaShop version -- : 2.6.1
-- Joomla version -- : 3.4.8
-- PHP version -- : 5.6.16

I have a product set that uses multiple custom fields ('A0','B0','K0',etc.). My customer would like to have a table display listing which is sorted by A0, then by B0, then by K0. Even though such a DB query is simple, the Administrative interface only allows a single value to be selected from a popup list. Is there a HikaShop approved method to sort product listings by multiple field values?

(I am a php developer and can modify code as needed.)

Found it. I added

if(!empty($pageInfo->filter->order->value) && ($pageInfo->filter->order->value=='b.ao')){
    $order = ' ORDER BY b.ao, b.bo, b.ko, b.k1 '.$pageInfo->filter->order->dir; 
}