use the populate list from array behavior on the Body tags onload event.
much the same way you add the populate list from array behavior to the parent select list on change event, only this time select the body tag.
Aslo use the Set Selected In List behavior.
the Body tag should have the following behaviors:
set Selected in list - to set the parent list selected element
Populate List from Array - to populate the child list
Set Selected In List - To set the selected item in the child list.