Is it permissible for my sister's husband to be absolved from his oath – by divorce – not to ride in her car, by selling it to him for a symbolic amount or by transferring its ownership to his name, knowing that my sister considers this a circumvention, and that he broke a similar previous oath under the pretext of anger and nothing happened after that?

It is not permissible to swear by divorce or anything else. Therefore, if the husband intended to prevent himself from the car, he must offer an expiation for a broken oath (kaffarat yameen), which is feeding ten poor people or clothing them, or freeing a slave. If he cannot find any of these, then fasting for three days. It does not require a contract or a dowry.