there is no way to execute a VBA function in an Excel workbook without opening the file...
Of course, you can prevent the AUto_open macro running by disabling events on the Excel Application object.
In Excel VBA we do this like so:
Application.enableevents=false
(frequently in conjunction with other settings like ScreenUpdating and DisplayAlerts)
in Java maybe you use:
excel.setProperty("EnableEvents", new Variant(false));
I hope that pointers you in the right direction (lol, boom boom !)
Philip