Just ask nicely. I’ve never ever had an issue, including at the likes of Manchester Piccadilly P13/14.
Exactly. It's not difficult!
"Tickets please?"
"I'm not travelling, my 90 year old Mum is on the train due from Glasgow in 5 minutes."
"No problem. Come back to me and I'll let you both straight out."
Or: "I've left my bag on the train from Liverpool yesterday, they said Lost Property is this way?"
"Yes, head along this platform and it's on the right."
I'd imagine conversations like that go on at gatelines and revenue blocks multiple times a day!
If someone is regularly coming up with a story, and regularly disappearing, then they can take it further. And presumably often do.
If it's a Compulsory Ticket Area, then platform tickets will presumably be available? If not, then on you go.