I've just stumbled across a description of the Windcheetah Andy Wilkinson used to ride LEJOG in 41 hours. It includes the following comment:
Feeding was a major logistical problem, rider consumption was an amazing 81 litres of fluid in 41 hours. This huge fluid intake also meant a huge output... We rigged up a special condom connected to a metre-long tube to provide relief for Andy without having to stop. The tube exited the Windcheetah at the rear of the fairing.
The ideal way to stop wheelsuckers?