Vista - excel & WSH question

Hello,

I have a question about excel and WSH. Here is the code I am using,

Dim xapp
Dim xbook

set xapp = WScript.CreateObject("Excel.Application")
xapp.WorkBooks.Open "xxx..."
xapp.visible = true
set xbook = xapp.activeworkbook.worksheets("yyy...")
xbook.activate

My problem is the following: normally when I open excel, I have additional
custom worksheet functions available through certain add-ins (namely,
Bloomberg). However, when I open the workbook with the WSH script, those
additional worksheet functions do not seem to load automatically, and the
custom worksheet functions are not recognized (they return #NAME?). Is there
an additional option I need to specifiy to get this to work? Any help
appreciated!

Thanks!
Kris