ComExcelConnect() creates a COM connection to a open workbook

ComExcelConnect.ahk

xlObj := ComExcelConnect( "ahk_class XLMAIN" ).Application

msgbox % xlObj.Range("A1").value
ExitApp

ComExcelConnect( WinTitle )
{
    objID    := "-16", objID &= 0xFFFFFFFF
    refID    := -VarSetCapacity( iid, 16 )
    iid_type := NumPut( 0x46000000000000C0
             ,  NumPut( 0x20400, iid, "Int64" )
             ,  "Int64")

    ControlGet, hwnd, hwnd, , EXCEL71, % WinTitle
    DllCall( "oleacc\AccessibleObjectFromWindow", ptr, hwnd, uInt, objID, ptr, refID+iid_type, "ptr*", pObj )

    return ComObjEnwrap( 9, pObj )
}