I've read that, which is what led to my question. From your post, it says "Discounts are valid only for coach fare for named HawaiianMiles member and their companion for roundtrip travel between North America and Hawaii booked directly through the Primary Cardholder’s HawaiianMiles account using his or her Hawaiian Airlines World Elite MasterCard and are subject to change."

From the fine print it appears I need to charge the full fare of the primary ticket onto the MasterCard. However, I've read some old posts on travel forums from tourists who signed up for the card just to get 75% off their airfare (the signup bonus covers 100% of primary ticket and 50% of the companion ticket). It seems they were able to use their bonus signup points to book an award flight and then use the 50% off companion voucher to cover half of the 2nd ticket. These posts were from earlier this year, so I'm wondering if maybe Hawaiian changed their policy.