ComboBoxItem and disabling an item

SmartGWT 3.1p

I have a LinkedHashMap with values as so:

"1", "One"
"2", "Two"
"3", "Three"
"4", "Four"

I have a ComboBoxItem on which I invoke setValuesMap(map).
All map items are selectable.

Later, I want to disable an item in the map from being selected; but, I would like to still show the item in the comboBox dropdown.

How can I disable an item in the comboBoxItem programmatically?

Richard