Comment by bell-cot

> ... no way to e.g. switch lanes in swimming so ...

Why couldn't you shorten the pool, from a swimmer's PoV, by putting (say) a very shallow plywood box against the wall of the pool at one end of each "non-center" lane? Yes, you might need to do some math & stats to figure out just how shallow a box. Or, you could use a feedback loop - boxes start very shallow, leading swimmers get to pick a lane, boxes adjusted, repeat.