Showing loading message in ComboBoxItem?

This is in SmartGwt 2.4

We have a ComboBoxItem that is backed by DataSource. Sometimes the number of possible items is large (hundreds). If you scroll down, you get an empty box while the new data is loaded from the server. Some of the users are bothered by this. Is there a way to put a data loading message in the rows like there is with ListGrid?