Offering Freebies with MarketPress

After attempting to create a free download using the MarketPress plugin I discovered you cannot set the sale price to $0.00. Upon doing so the price reverts to the non-sale price after clicking Update Product.

Is there any way to set the sale price for a digital product to $0.00 so it can be downloaded for free from the store page?

Case in point: We are offering a free sample chapter of a new ebook we are launching soon. The only way I could do this was to create a coupon code for the full amount of the sale price and instruct users to apply that code to download the free sample.

See example at:
http://agreda.com/store/products/income-anywhere-free-sample-chapter/

The problem, however, is that we do not want this coupon code to be applied to any other purchases once we launch the complete ebook and other items in the works. We would like to continue allowing customers to add this free item to their carts as we add new products. Any suggestions for how to do this are greatly appreciated.

Feel free to move this to feature requests if it is possible to incorporate this suggestion in a future plugin update. Thanks!