Originally Posted by
VaguelyCynical
I get an error with the online tool with any itinerary ending at a different location than it began (even though starting in JNB and ending in MRU is obviously permitted).
Since you're losing a segment by transiting LHR/LGW have you considered just flying LHR-JNB and then JNB-MRU? I know it's a four hour flight on a 737, but it seems to give you another option (as well as more miles) and you will have a long (more comfortable) segment on a 747/380.
Edit: I see your surface segment is BCN-LGW rather than simply transiting LHR/LGW. So obviously you're only left with that one segment so obviously my suggestion wouldn't work unless you could get to MAD rather than BCN. Just a thought. :-)