Maaseh Genaivah

Chaim B. posts here, here, and here on the topic of kim leh bdrabba mineih. The Rambam says in Hilchos Genaivah 3:4 that if a shomer slaughters an animal he is supposed to be watching on Shabbos, he is patur from the knas daled v'heh (the fine of 4 or 5 times the amount) because slaughtering on shabbos is chayav misah. Therefore we say kim leh bdrabba mineih and the genaiva and chiyuv misah come at the same time. Here is the loshon HaRambam:
ד] הייתה פרה שאולה אצלו, וטבחה בשבת דרך גניבה--פטור אף מן הכפל: שהרי איסור שבת ואיסור גניבה באין כאחת; ואם
אין גניבה, אין טביחה ואין מכירה
What is interesting about the lashon HaRambam here is that the cow is originally borrowed and then it is slaughtered "derech genaiva". What is the meaning of this? Can a slaughtering actually be a maaseh genaivah?
I found that the Chazon Yechezkel (Baba Metzia 3:6) quotes R' Chaim who attempts to explain the shitas HaRambam. This idea that the Rambam has that the slaughtering is a maaseh genaiva is actually based on a girsa in Baba Kama 112a that is mentioned by the teachers of Rashi. Rashi actually rejects the girsa on the grounds that if a shomer slaughters the cow he is watching he is not a ganav, but rather a gazlan. The proof is that the only way a shomer pays kefel is by a case of toan taanas ganav. This implies that in a normal case the shomer only becomes a gazlan. Rav Chaim explains that the real difference between a ganav and a gazlan is that a gazlan is when one causes the baalim to lose their mamon. However, ganav is defined by the added clause of lekicha b'issur. By a shomer the original taking of the object was b'heter. Now, by "stealing" it, it is only mechaser mamon habaalim, not lekicha b'issur, so it's gezailah and not genaivah. Rav Chaim suggests in the Rambam that a maaseh tevicha is considered a lekicha b'issur and therefore could qualify as genaiva if it is done b'derech genaivah (I assume he means in a secretive way). This explains the lashon HaRambam of derech genaivah.