This would probably work well. I can think of one problem. SNCF has a different fares structure though: they don't sell returns but sell two singles which are each valid for 24 hours after validation. In the UK return portions of Anytime Returns are valid for a month. So a passenger with (for example) an Edinburgh - Peterborough SOR could probably still get away with reboarding at Dunbar later in the month and validating their ticket again there saying that they had broken their journey there for a few days.