FixedTagalong.cs

// keep object in fixed distance to camera (including camera rotation - useful to place object for Hololens at the start of the application) 
using UnityEngine;
using System.Collections;

public class FixedTagalong : MonoBehaviour {

    Vector3 startpos;
    
    public float smoothTime = 0.4f;
    private Vector3 velocity = Vector3.one;

    void Start() {
        startpos = this.transform.position;
    }

    void Update() {
        // move cube to camera
        Quaternion toQuat = Camera.main.transform.rotation;
        Vector3 targetPosition = Camera.main.transform.position;

        // move according to start position
        targetPosition += Camera.main.transform.forward * startpos.z;
        targetPosition += Camera.main.transform.up * startpos.y;
        targetPosition += Camera.main.transform.right * startpos.x;
        
        // smoothly rotate and position in front of camera
        transform.position = Vector3.SmoothDamp(transform.position, targetPosition, ref velocity, smoothTime);
        transform.rotation = Quaternion.Slerp(transform.rotation, toQuat, smoothTime);
    }
}