Since no one can answer the question, I kept searching and trying for an answer and finally found one, so I wanted to share it with others who could have the same problem.
/** Set the collapse button to the right target. */
//Set the right id to the header/footer.
buttons.getParent().getElement().setId("header");
//You have to go up a few tiers in the DOM.
Element ep = buttons.getParent().getElement().getParentElement();
Element ec = buttons.getParent().getElement().getParentElement().getFirstChildElement();
//Change the data-target attribute to your id.
ec.setAttribute("data-target", "#header");