United will totally let you do this, actually. You simply look for the seats right behind the Economy Plus seats that don't recline, and buy them. I think they may cost more than other Economy Plus seats, actually. I presume other airlines are similar.

I wonder if any European airlines have non-reclining seats? I don't get to fly United often.

Ryanair has non-reclining seats, but that is more due to the fact that they pack their seats so tight that reclining would be impossible.

True, but I avoid Ryanair. I really don't like their corporate strategy.

Ditto.

I would also happily give up my ability to recline if it meant the person in front of me couldn't either.

Maybe aircraft with three distinct blocks of seats should have 1/3 which just simply lack recline. You want recline? Book the other 2/3 of the aircraft, I'm going to be booking that 1/3.

How many minutes do you think it will take the airline to work out that if the seats don't recline there doesn't have to be so much space between them and you can fit in a couple of extra rows.