Use of Dropdown layout element as listbox

I tried to use a dropdown gui element as list box, which essentially requires the dropdown list not to vanish on selecting an element. For this I subclassed Dropdown http://docs.unity3d.com/ScriptReference/UI.Dropdown.html and overrode creating the blocker, but then I tried to prevent the Dropdown being deleted by overriding DestroyDropdownList and calling show instead, but that does not stop the list becoming invisible.

Anyone knows how I can go about this?