Pivot Table Security in Excel

I have an excel file that I have created that contains a pivot table.
The file is supposed to act as a kind of 'pivot table template' The
idea is that a user could download this file from a server and then
open it and use it as the basis for creating a pivot table.

I have already created the datasource in the excel file, so the
dimensions and metrics appear in the field list as soon as the file is
opened. The problem I am having is I want to be able to restrict
access to the cube and potentially some of the dimensions by user.
But, if the datasource is already created and saved in the template
file then the next time the file is opened it just uses the existing
datasource.

I would like for Excel to force the user to 'login' or use their NT
information with the datasource so that when it asks Analysis Services
for the information for the pivot table it only provides the data that
the user has access to. I can't find a way to keep excel from saving
the previous login. I've tried making sure that the Pivot
Table-Options-External Data Source-Save Password is unchecked. It
still seems to retain the data the next time I open the file.

Any ideas on how I could force the user to login when the pivot table
information is accessed?