Non puoi.
Devi aprirti un DataReader sui campi che ti interessa mostrare, poi potrai popolare il combobox concatenando le colonne:
codice:
Dim OleDbConnectionString As String = <stringa di connessione al database>
Using conn As OleDbConnection = New OleDbConnection(OleDbConnectionString)
Dim sql As String = "SELECT campo1, campo2 FROM tabella"
Dim aCommand As OleDbCommand = New OleDbCommand(sql, conn)
Using aReader As OleDbDataReader = aCommand.ExecuteReader
cboFields.Items.Clear()
If aReader.HasRows Then
While aReader.Read()
cboFields.Items.Add(aReader(0).ToString + " " + aReader(1).ToString)
End While
End If
End Using
End Using