You are almost certainly right, at least from the technical perspective of what the rules say. I know of at least 2 cases of 'grey market' imported cars where taxes were never paid, however, so some people do indeed import used cars. Depending on one's willingness to test their negotiation skills, it may be possible in reality.
I hope you give this a try and report back. There's a lot of conflicting information here so it's hard to know what the real situation is. I've heard of people driving all over some continents in various vehicles and they some how get it done. One thing for sure is that the "rules" are merely suggestions in a lot of the countries you'd see along the way and that might mean its just a small bit of cash needed to solve the problems or it might mean insurmountable hurdles. Either way, it would be an adventure!
Thanks everyone. It's for a 9 year old so we can't use the mail-in passport renewal from the embassy.
However, turned out to be no problem at all at immigration. They gave him another 1 year as usual, so now we have plenty of time to renew the passport later.