Absolutely, this is exactly what I do. If you alight from the rear of a northbound train on P4 and walk along P3 to the stairs to exit your back is towards approaching trains.It's quite common for people to alight a train on platform 1 or 4 and then use 2 or 3 to walk down and 'jump the queue'. It's certainly more likely they'd be hearing a train horn than a member of staff shouting though. A lot of stations have PA systems with the volume very low, thanks to the local residents moaning and succeeding in having the volume cap. In those cases, if the PA won't work then you only have your voice.
The same applies alighting from the rear of a southbound train on P1 but fewer people do this as the majority of journeys are to/from London rather than the north.