I played around with this a little bit on Google Flights. Checked availability for the R/T LAX-JNB and ORD-JNB to see what days the lowest fares were offered. I then went to BA.com and did a multi-city search LAX-JNB and then JNB-ORD on the return. Be careful as the lowest fares that show (like $1500r/t) are using AA flight numbers so you get crappy returns on the EQD's.