Use this with a Unity camera set to orthographic projection in an oblique top-down view

StretchProject.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class StretchProject : MonoBehaviour {

    public Matrix4x4 originalProjection;
	Camera cam;
	[Range(1,2)]
	public float stretch = 1;
	[Range(0,0.95f)]
	public float squash;
	Matrix4x4 p;
	Matrix4x4 w;
	public bool squashAndStretch = true;
	void Start()
    {
        cam = GetComponent<Camera>();
		originalProjection = cam.projectionMatrix;
	}

    void OnPreCull()
    {
		cam.ResetWorldToCameraMatrix();
		p = originalProjection;
		if (squashAndStretch){

			p.m11 = originalProjection.m11 * stretch;

			w = cam.worldToCameraMatrix;
			w = w * Matrix4x4.Scale( Vector3.one - Vector3.up*squash);
			cam.worldToCameraMatrix = w;
		}
		cam.projectionMatrix = p;
    }

}