Earlier investigations into trading effects on influence suggested that goods being sold are already flagged with a system (or station?) of origin, meaning that all goods sold during one station visit, that were sourced from a single system, only count as one influence transaction. Buying goods from several systems and selling them during one station visit counts as several transactions. I don't know if that's still the case.
What is being achieved with this exploit isn't something that can't already be done to some degree between systems with large price differences, but becomes a problem because it can be done much, much faster between an FC and a station.
If they flagged goods bought from an FC with the system it's in at the time of purchase and reduced the influence effects of in-system trading, would that sort it out? I don't imagine that many people are using in-system trading at a profit or loss for influence purposes (but I could be wrong), so no great loss to existing mechanics. It would still allow trading with an FC to have an affect on influence but limit the scale of that effect.
Feel free to point out the elephant I've missed