A traveler going back and forth often, usually with minimal luggage. Could put a wheel in the checked-in suitcase every time.
Costs nothing, but to find such a person would be tricky.
Otherwise you could find someone who is emigrating from the UK to South Africa with a container full of belongings and ask them to bring the wheels along in the container. Also tricky to find, of course.
More traditional options would be literal shipping via a ship instead of air courier services.