MarketPress product downloads. Can you disable direct access to original uploaded files?

I uploaded a PDF which will be sold on my MarketPress site. It resides here on my server:
http://www.example.com/wp-content/uploads/2013/03/My_PDF.pdf

Once someone purchases the product, they are given this link like this to download:
http://www.example.com/store/products/book-1/?orderid=fa71699fcbfa

The unique URL for the order works great but I am a little concerned that the original file is still accessible *if* someone has the direct link. I know it's not likely but I am curious if there is any way to lock this down?

Thanks