Disabling The some of the Dropdown items

Hi,
We are using SmartGWT 4-1 pro (Nightly Build :2014-07-09).
We have a requirement like disabling some of the items in SelectItem.

1. We have a Select Item.
2. We have added a value map to Select Item.
SelectItem sampleSelectItem = new SelectItem();
LinkedHashMap<String, String> sampleMap = new LinkedHashMap<String, String>();
sampleMap .put("itemKey1", "Item-A");
sampleMap .put("itemKey2", "Item-B");
sampleMap .put("itemKey3", "Item-C");
sampleMap .put("itemKey4", "Item-D");

sampleSelectItem.setValueMap(sampleMap);

Our requirement is some of the Items has to be disabled, what I mean to say is, the user able to see the items but he can not select that disabled items from the Select Item.
Here I want to disable "Item-A", "Item-B" on UI.
Is there any API to disable the select items from user selection.
Please give us a solution for this requirement.


Thanks.