ListItem add to comboBox

Hi,

I am working on C#.Net project with infragistics. My project i want to implement search options, like Microsoft office Outlook 2007 Instant Search functionality. For that i am using UltraComboEditor.In UltraComboEditor i have added 3 ValueListItems(Search all screen, search current screen, search options). I want to add one more items "Resent searchs", but this item should be list items, i dont know how to add one more listitem into UltraComboEditor.

Thanks