From: Rabbi Moshe Sofer
To: Rabbi Simcha Bunim Ginz (Eiger)
The Chasam Sofer resolves the tension between the Ramban, Ran, and Bach — who hold agency cannot apply to vows and hekdesh — and the Gemara in Nedarim 36a, by distinguishing between initiating a new verbal obligation (not delegable) and executing a preexisting obligation through a physical act (delegable). He further argues that a mumar, unlike a gentile, retains the capacity to serve as an agent because he can repent at any moment.
Source: Shu"t Chasam Sofer YD §321