Or you could go the gift certificate route: if the event you want to have catered is still a couple of months away, you could buy GF's starting this month, and each next month till the event, for the maximum miles earning amount ($600 or $1000 apparently) and use the GF's to pay the catering.
Of course this only works if there are still a couple of months to go before the event and if the restaurant accepts GF's for catering.
Some checking is recommended (also on finding out if that restaurant's GF's will earn you miles).