It's possible to buy tickets in advance, or online, or have two season tickets bought at each end - you might need one single the first time you did it.
I take your point. Although, the type of person who my suggestion is aimed at really wouldn't be smart enough for sitting down and figuring out 'on paper' what tickets to buy to obtain a lower fare.
You're kidding me? There is still plenty of fare evasion on the Underground, even from and to barriered stations (a small number of stations are either partly or wholly ungated), with either, as 'Steve Ford' says, people doubling through, jumping over, use of counterfeit tickets, misuse of passes or tickets that allow discounted/free travel, use of a ticket/tickets to get through gates but does not cover the full journey length, and so on.
Maybe I shouldn't have said 'no' fare evasion. But it would be significantly reduced. I find tailgating unlikely to happen as much as on LU, as ScotRail's gates are pretty closely watched (and are quicker to close than LU, I've noticed). Counterfeit tickets, should they become widespread, will be surely be picked up on by the TOC and it quickly clamped down upon as well.
I still think evasion would be significantly reduced by gating all the stations though. I make around 15 journeys a week on this route. Out of those, I'd say just over half of them have kids/neds running down the train (or off the train and down the platform) to actively avoid a ticket check. Huge, huge problem.
Maybe a quick point for you to address given your counter arguments to my suggestion: how much do you think Glasgow Subway loses due to the reasons you've suggested? Say, as a percentage of total passengers, how many do you seriously think have evaded the fare, and how? This is the model they run - all stations gated, all stations staffed with ticket office overlooking a gateline. No inspections on train.