Virgin Atlantic Flying Club - Booking multi-class round trip?

How does one book a multi-class roundtrip on VA? I want to fly UC, IAD to LHR, but return on PE. For some other airlines, including VS (!), the booking engine shows all the fare classes, but I am not finding this option on VA. One alternative would be to book 2 one-way tickets (UC eastbound, PE westbound), and hope that would not be more expensive. Please advise. Thanks.

In the booking engine click on More Options and you'll see per sector booking fields, where you can select UC one way and PE the other.

In the booking engine click on More Options and you'll see per sector booking fields, where you can select UC one way and PE the other.

Thanks! I would not have guessed that from the website. That option works, and after a few tries, I was able to find suitable combinations at various price points.