We don't usually use this forum to sell code but ...
I don't think there's a native way in Excel or PowerPoint. We have an SAddIn that can insert data from a csv file (easily made from Excel). It's not free but won't break the bank either. If it doesn't do what you need just ask for a refund.
Or of course you could write your own code.
http://www.pptalchemy.co.uk/Simple_merge.html