I need to book an open jaw PHL-CPT NBO-PHL

All flights are operated by BA (BA68, BA43, BA64, BA67)

Can I somehow book PHL-CPT in WT+ and NBO-CPT in WT?

BA.com quotes me $1,406 for WT and $4,385 for WT+.

Can somebody quote a mixed cabin itinerary (if it's possible).