Personal mission to alert middle lane drivers to their errors. Couple of bursts of high beam then outside lane and cut back in (safety) across the middle lane to the inside to highlight correct motoring. I wouldn't recommend undertaking.
....That's exactly what I sometimes do (providing, like you, the conditions allow doing so safely and with plenty of room). But it's amazing what a small percentage of drivers take any notice and they continue plodding on in the middle lane. I expect that some of them even say to their passengers: "Look at that fool, changing from lane to lane!"
Approaching them fast from behind can get them moving lane but it's not something I like to do.
You can lead a horse (in this case a donkey) to water but you can't make him drink.