I remember reading somewhere a while back that if I am short some miles/points for a redemption, I can use whatever I have and owe the reminding miles/points. Does anyone remember which program/credit card this was from?

For example, I have 40k miles/points and I want to redeem 50k. I can reserve it for 50k and owe 10k.

Maybe I'm wrong.. but I thought there was something like this.

Thanks.