This is an area that seems to be very mixed in terms of how it is treated (experience from many phone calls over the years trying to nab 15a/k on 772s! and it is as far as I can tell a very soft benefit.

Funnily enough, tonight when I discussed for a future WTP flight, the GGL agent said that the "new system" should mean that they couldn't do this any more, although it may work occasionally and advised not to phone in at T72. I think i will based on the above as it still seems to be pot luck.