In the handful of cases where I've seen pax vacate the exit row (usually due to small kids being in the party, sometimes due to lack of English skills), the FA has asked customers forward of the exit row, in E+, if they were willing to switch.

Of course, with a POS/COS in the row, it might be harder to find volunteers. Although I suspect some of the potential volunteers wouldn't be smart enough to look behind them and evaluate the space situation before saying yes.

I love DenPremEx's basic idea of the get-of-jail-free-card though and will have to remember it. I'm an exit-row-window kind of guy, so getting a POS in the middle leaves me squished up against the outside wall, which is worse than if you are in the aisle with a POS in the middle. In an extreme case, any other seat, including E-, would be better than being stuck in half of an exit-row-window.

I have always maintained though, that on a full flight, the only correct answer to the problem of not getting the entire seat you paid for is IDB compensation. Haven't had to test that yet though.