You either misunderstood what they told you or you need a new accountant.
There is no way an expense = revenue. What I would do is set up a "promotional item" expense account to record this item.
The easiest way to handle this is to record it as a non-inventory item using a "promotional expense" account. When you make a purchase you credit cash and debit the promotional expense account. If you want to track this item as inventory make it a "Non-inventory item" setting up the cost as .30 cents and the selling price as "0.00". Make sure you set the expense account to promotional expense.
You do not have to "show proof" it was a bonus. All you have to do is not record any revenue from the "sale". It is just a promotional expense.