Is this scenario worth using a GUF1 for.

Got 2 x GUF1.

Contemplating something like DUB-LHR-TYO or to HKG first and then separately up to Tokyo using Avios.
Could I ring BA up and book DUB-LHR in ET and LHR-HKG in CW and then apply the GUF1 to the booking to give CE and F? Should save around 34500 Avios + £200? taxes if possible.

Going to use my other GUF1 and 2 for cash bookings later next year.