Just got a thought...
Thought you dont have access to the DataView before binding...still that dataview is available in DataSource property of the combo...
// combobox bound to dataview here
// now it is available in DataSource property
DataView dataView = (DataView) comboBox1.DataSource
DataTable dataTable = dataView.Table;
// Now add new row to DataTable with the old value of WellType
// this will automatically update the combo box.
See if this will work for you.