There are two ways to do this, as I mentioned in the above thread: either let those 'in the know' do it, or take a militant approach. The latter means staff can't travel either.
The militant approach wouldn't be sustainable, at least from a staffing perspective. Most of our drivers and guards live in the first commuter town and use trains with pick up/set down limitations in the reverse sense.
Knowing them, half would ignore platform staff and board/disembark anyway, and half would wait for the next train and book on late, making it clear why. That being said, platform staff wouldn't enforce it anyway. The whole thing would converge toward bad feelings, disciplinaries and probably union action.
The problem is that although rail staff are officially bound by the same rules as fare paying passengers, in reality it's a very unliked guard who chucks another TOC's staff off, or a despised platform member who would stop staff from leaving a 'pick up only' service.
I've worked in various roles on the railway, and I can't remember a single time when a flash of my I.D. and a smile hasn't got me on a train for free. I've always been ready to pay, but never had to. Although unrecognised, it's a hark back to the railway family of the BR days, and I think it's quite nice honestly.