KLM and a few other airlines used to be very good in this respect - accomodating passengers on the jump seat at the Captains discretion if the cabin was full and the flight overbooked, if nothing else it was excellent
PR .
I find it hard to believe they'd still do it as although they're not a UK based airline they have a big market share at regional UK airports in terms of interlining and if they did have this policy when no one else did it would harm their image as a security concious company.
Even as an ATCO it's next to impossible to get a jump seat ride for the purposes of TRUCE and never as a passenger.
As you say, Chinese whispers etc.