There is plenty of information on the oneworld forum regarding getting RTW tickets originating in Cairo, which as LHR Tim has pointed out would be cheaper for F than you have already paid for CW.

It will involve some hassle with ticketing and and a visit to Cairo to start the RTW but given the savings you might feel it is worth it. You should be able to get a full refund (if you have already paid) on your existing tickets according to the fare rules. Thanks Gaza and ScottC