So playing with the API, figured out you could specify multiple stock IDs and get back stock information for all of them by comma delimitating it.
When you try this on the /users/ route however you get the following PHP error:
http://api.torn.com/user/1,2,3?&key=Fatal error:
Call to a member function useBonus() on a non-object in /torncity/html/casino/modules/companies/classes/bonuses/companiesBonusWrapper.class.php on line 57