On a OWE, you must include Europe if you go to Africa, as there are no flights from the Americas to Africa.

Have you considered a Star Alliance RTW? Beginning in March, you can use SA on *A RTWs, and that would presumably solve your issues of traveling within Africa (SA has JNB-DAR flights), as well as offering direct flights between South Africa and the U.S. *A has different rules (one of the most significant is that you can't stop over more than once in the same city), and it's mileage-based rather than continent based.