Don't know if I can help you, but are you knowing the method below?
This method will be called before the site is displayed ant the Object you can return is your command object.
protected Object formBackingObject(HttpServletRequest request) throws Exception
I'm using both methods. For data outside my command, i fill in a map in the method referenceData and for the other data, i use the method formBackingObject.
Don't know if this is the right way but it works for me. And perhaps I can help you with this information.