United MileagePlus (Consolidated) - Combining fare classes on UA itinerary on (mostly) SA metal

Hi
I'm trying to buy a RT NYC-JNB-CPT-JNB-(FRA or LHR)-NYC ticket on the UA site and to take advantage of both the 150% EQMs offered on SA metal in S&Q class and to be eligible to use a GPU on the one UA-metal segment on the way back.

The roundtrip in S prices at just over $1500, but the FRA/LHR to NYC segment in S won't be eligible for a GPU. When I exclude S from the search I see a similarly priced ticket (outbound in L, return in Q via FRA for $1570)

Is there any way to combine the 2 and assemble an itinerary with the outbound JFK-JNB-CPT in S and the return CPT-JNB-FRA-EWR in Q?

And if not online can I call them and ask to do over the phone?

thanks a lot

...And if not online can I call them and ask to do over the phone? .... Phone agents can build itins with any available fare class for each segment -- can not do that online. Note the fare rules may create fare breaks if combining arbitrary fares class -- so pricing will be hard to predict in advance.