I did vote also for this function because I just tried the same.
Btw.. I'm working also with rich:pickList where I tried to disable as well without success:
1. disabled attribute has no effect on pickList
2. There is no way to remove the copy buttons (only the labels can be removed)
3. the double click is cannot be disabled
@Ilya: Maybe you could expand the change request a little bit to cover the pickList aswell?