Trying to be practical here and thinking about how to make the total picture better, which might also help some folks here. Since I have two stays already booked and 3 rewards to use, I partly solved the problem by purchasing one comp night at Aria reward.
This saved me $80 net by rebooking the rest of my Aria stay at Priceline (for one less night), and came at a cost of 100K LP. Since I cancelled one $100 freeplay, I saved 250K LPs and lost only $20 in advantage. If you play the freeplay through slots, then it doesn’t seem like there’s any advantage loss. So one might argue that this deal made the bottom line even better due to LP savings.
So, I’ll do $150 FP at MB and $100 FP at Aria and the third award will be my one night at Aria and be done with it. Hopefully they won’t oppose my $100 FP at Aria, stating that I booked it via third party. Oh well.