A postscript to my last post for those who are interested.
For G+Y HYD failure, A/THR is available and used.
For G+B HYD failure, A/THR is available but the QRH/FCOM3 directs it must be switched off for the approach. I understand this is to prevent handling problems due to loss of multiple flight control surfaces, in particular L ELEV and L+R AIL, both of which are controlled by G SYS and B SYS.