Delete Group Items of ComboBox in Rhino


I am working on a plug in for Rhino. So far I have, among other things, created a RhinoOptionsControl and put a combo box (CRhinoUiOptionsListCtrlGroupComboBox) in it. I have added some items to it and all seems to work well. Now I need to dynamically add and delete items to the combo box, however I have found no way yet to remove items from it. Is there any way to do this?
So far I have tried deleting items using classes of the CComboBox parent class which does not work and rebuilding the entire GUI when something changes which is quite slow.
Is there any way to do this? Thank you in advance.

@JohnM - I this something you can help with?

I’m pretty sure that CRhinoUiOptionsListCtrlGroupComboBox::PopulateComboBox() is called when the item is clicked on which is the location you should use to populate the combo box. Clicking on a different item in the options list destroys the combo box and its contents. Clicking on the combo box again will create a new instance of the control and call PopulateComboBox().