CRM: Trigger Lead Assignment Rules on insertRecords Method

CRM: Trigger Lead Assignment Rules on insertRecords Method

I've been looking through the docs and can't seem to find a way to trigger the lead assignment rules when the insertRecords method is called via the API.  This seems like it should, logically, be triggered using the wfTrigger flag, but I've only been able to change the lead assignment manually through the API.  Additionally, there doesn't seem to be a way to write a Workflow rule to handle the lead assignment.   

If there is a way to utilize the lead assignment rule via the API or could someone point me in the right direction to use Workflow rules to accomplish this task?  Thanks!