Basically, Bill points to the gospels' claim of an otherwise historically-unknown custom of freeing a prisoner. The crowd chose a rebel called Jesus Bar Abba (Jesus, son of the Father) rather than the healer, Jesus of Galilee. Bill notes that the crowd would be likely to choose someone who walked the walk (the rebel) over someone who talked the talk (the healer).
He also notes
At it's largest, there were about 10,000 in an empire of 60,000,000. If Jerusalem had as many as 65,000 inhabitant (I think your 25K number is way low), you're looking at about 11 equestrian families, maybe a few more since it was a regional capital.Bill, yep, if there were two Jesuses there, the rich would most want to get rid of the "walk the walk" guy because he's the greater immediate threat, but you could argue as easily that the crowd would prefer to free the healer. After all, both Jesuses lost, and the healer lost just for talking, while bar Abbas is presented as a thug.
Those guys (at least the ones who were not also part of the political classes) would have kept FAR away from anything involving local politics.
But I think the gospel writers were confused, that there was only one Jesus, because the healer Jesus was constantly talking about being a son of the father ("Abba"). As you note, there's no example anywhere of Jerusalem's leaders giving the crowd an opportunity to pardon anyone. The story of two Jesuses is just odd. Wikipedia points out two more problems with the story: "The corresponding verse in Luke (Luke 23:17) is not present in the earliest manuscripts and may be a later gloss to bring Luke into conformity. The gospels differ on whether the custom was a Roman one or a Jewish one."
Now, I hate arguing with people who generally know a subject better than I do, but I'll continue to think the crowd was primarily rich or paid by the rich for these reasons:
1. The Romans weren't popular. They were only loved by the rich Judeans who adopted Roman ways, the ones who exercised nude and cut their hair and wore their clothes in Roman fashion. After all, Jesus’s revolt happened during a time of many revolts, near that of Theudas, midway between that of Judas the Galilean in 6 AD and the First Jewish-Roman War from 66-70 AD. Most Jews wanted the Romans gone just as most Iraqis and Afghanis want the US gone.
2. From every historical account, Pilate was a brutal governor. Even if he staged some kind of show to get some of the local Jews to take responsibility for killing a rebel, he was not hesitant to kill. He didn't seem to learn from his mistakes--he was finally recalled for being too harsh to the locals.
3. Far from wanting to seem non-political, the rich people of Jerusalem would've wanted to show their loyalty to the empire.
4. No empire worth its name lets the locals fuck with bankers or tax collectors.
5. If the Romans spared Jesus, they knew he would pull the same shit again.
6. The crowd probably was a mix, ranging from the children of the rich (think of the university kids who protest both for and against wars) and crazy people and people who just wanted some excitement and people whose allegiances were with the rich because they worked for rich people and people who wanted to suck up to the Romans and maybe people who had been paid by the rich to make a show of Roman loyalty. But the only people who benefited from killing Jesus were the rich who allied with Rome. To the people, Jesus was Robin Hood or Dick Turpin, not someone who deserved death.
Basically, if you're trying to imagine the crowd calling for Jesus's death, think of who shows up for Tea Party events. Sure, they're not all rich. But most of them are richer than the general population, and what they're advocating only benefits the rich.
ETA: The Tea Party isn't a perfect example of rich people demanding things that will benefit them. See Tea Partiers Are Fairly Mainstream in Their Demographics and Who Are the Tea Partiers? But they're a very good example of people being directed by the rich: Corporate Lobbyists Raising Money For Tea Parties.