Rav Menasheh says that the thief throws the animal over the wall in such a way that the animal will be able to run in front of the thief. However we know from gemara bava kamma, (brought in Rashi Mishpatim) that a thief pays 4 times, as opposed to 5 times, for tevicha and mechira for a sheep, because he carries it through the streets, whereas Rav Menasheh indicates that the animal runs in front of him.
yitz, lakewood, USA
My initial response was that the Gemara is talking about rams ("Dichrei"), whereas the Gemara in Bava Kama mentions specifically "lambs." Although such a distinction would be a big Chidush, it seems perfectly logical to apply it. I then found that the Toras Chayim, who begins his comment by stating that the Gemara here is not confined to rams but extends to lambs as well (indeed, the Rambam cites the Halachah with regard to lambs), deals with the problem. Clearly, he, too, had my distinction in mind (and perhaps it was the statement of the Rambam that forced him to discard it). After establishing the Gemara by the case of a lamb, he then asks your Kashya from Bava Kama. He answers that Raban Yochanan ben Zakai (in Bava Kama) is discussing the time of the theft, when the thief needs to make good his escape. Once he has left the owner's domain, however, he is in less of a hurry and will prefer to place the lamb on the ground and let it walk.
Incidentally, I wonder why the Gemara attributes the thief's careful treatment of the animal because he needs to walk it in front of him, and not to the fact that if he renders it a Tereifah, he will have caused himself a loss, since he will then be forced to sell it to a Nochri at a reduced price. That, too, would solve your problem. Perhaps the answer to this is that the problem of how to transport the animal simply precedes, chronologically, the question of what he will subsequently do with it.
B'Virchas Kol Tuv,
Eliezer Chrysler