If you can seperate 2 runners you can do that with 16 runners. Seperate into 8 lots of 2, eliminate one from each and then 4 lots of 2 and repeat above until 1 runner is left.

Other methods for splitting 2 runners might include the best 600m time [or best averaged], the most prizemoney last prep. or more simply the horse who has won the biggest 1st. prizemoney last prep., the best trainer and out of left field, pick the horse that is having a gear change [if applicable] or the one that has traveled the longest distance from it's home track to race.

Cheers.