Refresh data from services based on current user credentials

Question

Hi Guys,

I'm doing a POC, generating graphs & pivot tables using PowerPivot 2010 for SharePoint. 

My requirements are, 

1. Getting user specific data when the user logs in to the SharePoint environment.
2. If the above option is not possible, I should be able to filter the data using a user specific flag - can be a role/username/bit value.
3. The SharePoint may be hosted using Claims authentication. 
4. Services are basically REST services which are protected by a cookie based authentication.

I understand the following are the constraints in using PowerPivot for SharePoint.

• PowerPivot can refresh the data and store the it in the Excel workbook using a credentials configured either in the ConnectionString, connection manager or SSS ID. Hence points 1 (above) is not feasible.
• I'm unable get the user name of the current user in PowerPivot. This can be done using VBA or VSTO - but hosting VBA is not feasible in SharePoint. 
• SharePoint should use Windows Classic authentication.
• Is it possible to write a wrapper around the PowerPivot / Excel services to bring the data on the fly from a data source?  This will allow me to retrieve to any sort of services/databases.

If the above are shortcomings of PowerPivot 2010, are they being addressed in PowerPivot 2010 (with SQL 2012)?

Appreciate any help/direction on the implementation.

Thanks,

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Anbu