Android In-app Billing "Un-purchase" for testing?

My alpha testers can perform in-app purchasing fine.

I want to add an element to an already existing one-time purchasable upgrade. For instance, the one time upgrade already includes "power up A", but I want to also include "power up B" with the upgrade.

Since all of my alpha testers have already purchased the in-app upgrade in a previous version of the app, I can verify that they now have access to power up A and B... but how can I set my alpha testers back to "un-purchased" so I can simply test the purchase process flow without resorting to bogus email accounts or some other rube goldberg work-around?

I see no mention of this at android in-app billing sandbox

How do I un-purchase in-app upgrades for testing purposes?

Thanks!