The gemara tells of arabs who gave money to purchase a part of an animal that was to be shechted by a jew and questions whether there is concern that the arabs intent to have his share shechted for avoda zara would invalidate the entire animal. The gemara says that if the arab is strong in the sense that the Jew cannot break away from him, then the animal is assur, but if the Jew is able to break away from him it is mutar. Rashi explains that if the Jew is able to break away from the arab then - אינו נעשה שלוחו על כרחו, the Jew doesn't become an automatic agent of the goy to assur the animal, but if the Jew is is unable to break away, he serves as an agent for the goy to assur the animal. Rashi seems to understand that the concept raised by the gemara of זה מחשב וזה עובד works as shlichus meaning that the shochet serves as the shliach of the owner as if the owner himself were actually shechting for avoda zara. The Maharatz Chiyus raises a question that the concept of "shlichus" between a jew and a goy doesn't exist. The gemara in Baba Metzia 71b derives from a pasuk that there cannot be any shlichus between a Jew and a Goy in either direction. Based on this, how can we apply the concept of shlichus to make the animal assur?
Rashi in Baba Metzia concludes that we do consider their to be shlichus between a Jew and a Goy l'chumra. This helps to explain Rashi in Shabbos 153a. Rashi explains the gemara's question as to how a Jew could give his money to a goy to carry as shabbos is beginning, that it should be assur because the goy is serving as his shaliach. Rashi seems to understand that the concept of amira l'nachri is based on the goy serving as the shaliach of the Jew. The Shulchan Aruch HaRav articulates this point clearly:
הגר"ז בס' רמג ס"א וז"ל אסרו חכמים לומר לנכרי לעשות לנו מלאכה בשבת וכו' שכשהנכרי עושה בשבת הוא עושה בשליחות הישראל ואע"פ שאין אומרים שלוחו של אדם כמותו מה"ת אלא בישראל הנעשה שליח לישראל וכו' אבל הנכרי אינו בתורת שליחות מה"ת, מ"מ מדברי סופרים יש שליחות לנכרי לחומרא עכ"ל
Therefore, it is possible that in our context also, Rashi will hold that m'drabonon we are machmir to consider the Jew a shliach of the goy, whenever the Jew doesn't have the ability to break away from the goy. In truth, Tosafos also writes that the issur on the animal when the Jew can't get away from the goy would only be m'drabonon (but Tosafos seems to say that it is only d'rabonon because there is something lacking in the s'michas da'as). It seems that Rashi would hold that the entire issur on an animal shechted by a Jew when the Non-Jewish owner had intent for avoda zara would work through shelichus and would only be assur m'drabonon. Another possibility is that when money exchanges hands we could consider a goy to be a shliach of the Jew or a Jew to be a shliach of the goy. This is the sevara of the machaneh ephraim in the context of a goy building a ma'akeh for a Jew and allowing a Jew to make a bracha - יד פועל כיד בעל הבית דמי. Therefore, in our case where the Jew accepted money from the goy and cannot break away, even m'doraysa he may be his shaliach.
The Rashash explains the concept of an איניש אלמא who the Jew cannot break away from based on the Rambam in Hilchos Chometz U'matza (4:4) that when the Goy will be able to force the Jew to take responsibility for the chometz, the Jew is obligated to be destroy it before pesach as if he willfully accepted responsibility. Here too, since the goy can force the Jew to maintain the partnership in the animal and prevent the Jew from breaking away, the machshava of the goy qualifies to assur the animal.