I tried to use Leslie's idea today - we could buy Premium Economy on BA for $2,434 and upgrade to Business for 45K miles apiece, but the only return dates from JNB were either 9/24 or 9/30. If we only upgraded on the way to CPT the fare would have gone up to $3709 because the lower fare isn't available in Premium Economy on the return on 9/26. I'll keep checking but I think we'll be flying Virgin Atlantic when those fares open up. Seems to be the best deal around right now.