Assuming I understand your use of "already" here, I don't think you can do any better than ExecuteInEditMode combined with Application.isPlaying (maybe). In particular, there is no equivalent to Update() for editor mode in terms of a function that is called every frame even when nothing changes.
One thing you haven't specified, though, is how you associate an object with a path it is to follow. If I were coding this then the GameObject would have a path field specifying the path it is to follow. If that were the case you could do something like this:
using UnityEngine;
[ExecuteInEditMode]
public class MyComponent : MonoBehaviour {
public CircularPath path;
void Update() {
if (Application.isPlaying) {
// Do whatever we do when the game is running
...
} else {
if (path) {
path.snapToPath(gameObject);
}
}
}
}