I can't imagine for a moment that DJ will adopt the Virgin UK scheme. FWIW.
A far simpler system is more likely, such as the Southwest one I mention above - 1 free flight per 10 paid etc.
Cost to DJ is then near nil for all awards as all awards are capacity controlled on part empty flights.
I rented a car this week from Euro cars and they had a sign there saying anyone who rented in July and August and showed a DJ ticket would get free entry passes to the Virgin Blue Rooms.
We had QF tickets, but as always, I cheekily asked if girl could swing us a couple, but said she needed to add the DJ flights numbers to computer to generate them, but it was a nice offer. ^