Kustow made his debut in the Ski Jumping World Cup on December 30, 1988 at the opening event for the Four Hills Tournament 1988/89 in Oberstdorf . He was able to win the first World Cup points in this first competition with 14th place. In the remaining three competitions, however, he was unsuccessful. At the Nordic World Ski Championships in Lahti in 1989 , Kustow jumped from the normal hill to 12th and from the large hill to 34th place. In team jumping he reached 4th place with the team. On January 14, 1990, he was able to jump on the podium for the only time in his career in Liberec and finished third. After further good placements, including a 4th place in Sollefteå , he finished the 1989/90 season in 21st place in the overall World Cup ranking. In the 1990/91 season , however, he could not win any more points and ended his active ski jumping career after the end of the season.