You could also investigate the IAH-DOH-CPT route on QR - IAH-DOH is run on an AA codeshare which would yield you EQM and RDM just like an AA flight. DOH-CPT (stops in JNB) unfortunately does not appear to have an AA code on it, so that'd be lost mileage.

It also requires an overnight in DOH which is probably not ideal unless you are looking to break up the trip duration a little.