Hi,
Use the Live office to embed webi reports in the PPT.
Checked the option fetch data from latest instance.
This will work when you have scheduled the reports and same time when you will open the report in PPT , reports will display latest instance of webi reports in PPT.
To use this Live office should be in the client machine.
For more information check live office guide.Search the Latest instance in the PDF and you will get the information on this option.
http://help.sap.com/businessobject/product_guides/boexir31SP3/en/xi31_sp3_lo_user_en.pdf
Regards,
Amit