It’s simple. Throw in a pacer through halfway for each race in the 3k/5k groups and don’t prescribe them world record pace or anything, but something that everyone in the field should be capable of; say 13:30 for the men and 15:00 for the women. Then, the race has to be won in under that time or everyone has their prize money cut in half. Furthermore, if nobody goes with the pacer and he/she decides to stay in and win the race in UNDER the prescribed time, the pacer wins half of the prize money for the whole category.
I see this as adding a lot to the format. First, it adds another body on the track in these awkward, 8 person long distance races. Second, it gives the racers/challengers more incentive to run an honest pace rather than the absolute slog we saw for the men’s 5k on Friday. Finally, it adds another level of tension to the races and an underdog (pacer) for the crowd to root for.