I really have wanted to have slalom night events for so long, but we just stick to the fun rounds too. The best we ever did was clear duct tape and color coordinated glow sticks taped to buoys. We found out you have new buoys that have no algae build up otherwise the duct tape will not hold.
The fun thing was we had all kinds of extra glow sticks too. You can actually put them inside of the slalom rope, light up your soap bottles and tape them to skis.
This year we are going to do the event and rent a dance floor so its going to be more than just skiing. Yee haw!