No, this particular use would not work. Because a borderline is cast to separate "self" from "other," it cannot be cast on a shinki's own body.
However, it would be possible to cast a borderline on a moving object, such as a stick or a handle, and move it around the body to defend without re-casting. It would take a great deal of practice and concentration to maintain a borderline on a moving object.
Re: Borderline forms
However, it would be possible to cast a borderline on a moving object, such as a stick or a handle, and move it around the body to defend without re-casting. It would take a great deal of practice and concentration to maintain a borderline on a moving object.