Setting the AssignmentRuleHeader

I need to set my submissions to use the default assignmentRuleHeader. Ideally, it would just be a checkbox on the fieldmap page sort of like it is if you were to fill out the lead form on SF.com.

Looking at the module, maybe I can just add this during the presave hook.

Is it as simple as tacking on to the $object another object, AssignmentRuleHeader->useDefaultRuleFlag = True and handing it back to sf_webform?

Thanks,
Colin