The airlines, however, have to follow international regulations and I'm afraid he cannot count on his luck and charm (some nice lady, enchanted with WarsawNoob's smile, letting him board the plane without a passport).
Actually, I don't think the airline is obliged to check. The low cost airlines do so in order to prevent people from passing tickets onto someone else - and all carriers to the UK will check because of the threat of a 2000 pound fine for bringing someone to the UK without the correct documents. But apart from that, they're under no obligation to actually check when intra-Schengen as far as I'm aware?
And I read somewhere that the driver's licenses (American or European) are NOT considered ID cards for the purposes of border crossing or even personal identification abroad, so you need your passport even in Poland when the police has any questions to you.
They aren't, but for the purpose of identification when within a country, they're good enough.