KARFA

I guess something like MUC-LHR-AMS return in ET would be fairly cheap and time efficient and get you your four sectors. You would have to book as two one ways probably since turnaround at AMS is usually lower than MCT preventing you booking it as a return. Also AMS is very easy to do a b2b.

Also bear in mind your eligible flights can be BA codeshare flight, or IB operated & marketed flights in case you would prefer a trip to MAD.