You would have to fly IB to/from CAI, forcing you to have surface transits in Europe. So your routing would be CAI-MAD (or BCN)/LHR-DXB-LHR ... MAD-CAI (as you must end your RTW in the country of origin). Cannot buy extra segments in continent of origin, so you are stuck with these segments if you want to do LHR-middle east and originate in CAI.