FakeRenderTexture

using UnityEngine;
using System.Collections;

public class FakeRenderTexture : MonoBehaviour {
    public Texture2D texture;
    public float updateFrequency = .5f;
    private float lastUpdate = 0f;
    private Rect sourceRect;

    void Start() {
        sourceRect = new Rect (0, 0, texture.width, texture.height);
        camera.pixelRect = sourceRect;
    }

    void OnPostRender() {
        if (Time.time > lastUpdate + updateFrequency) {
            lastUpdate = Time.time;
            texture.ReadPixels (sourceRect, 0, 0);
            texture.Apply ();
        }
    }
}