If anyone is curious, i added a combo box to a toolbar instead. I created the combo box manual, and made sure there was room on the tool bar for it.
I added ID_SEPARATOR to the buttons array and called setButtons:
m_ChartToolBar.SetButtons(buttons, sizeof(buttons)/sizeof(UINT))
m_StudyComboBox.Create(WS_VISIBLE|WS_CHILD|ES_RIGHT|ES_READONLY | WS_VSCROLL|
CBS_UPPERCASE,CRect(190, 0, 300, 100),
&m_ChartToolBar, 3)
Hope this helps anyone that is interested.