Change 3D perspective while scrolling - fixed vanishing point

Question 1

I know it is to late for the OP, but for all others coming across this question:

I was able to solve it by using a <div> inside the body that is emulating the body's scrollbars.

<html>

<head>
  <style>
    body {
      padding: 0;
      margin: 0;
    }
    body > * {
      overflow: auto;
      width: 100%;
      height: 100%;
      position: absolute;
      perspective: 1000px;
    }
  </style>
</head>

<body>
  <div>
    3d objects
  </div>
</body>

</html>

Full example:

<html>

<head>
  <style>
    body {
      padding: 0;
      margin: 0;
    }
    body > * {
      overflow: auto;
      width: 100%;
      height: 100%;
      position: absolute;
      perspective: 1000px;
    }
    div#container {
      width: 200%;
      transform-style: preserve-3d;
    }
    #t,
    #b,
    #l,
    #r {
      margin-left: 45%;
      margin-right: 45%;
      width: 100px;
      height: 100px;
      background-color: yellow;
      border: 10px solid black;
      border-radius: 10px;
      transform-style: preserve-3d;
    }
    #t {
      transform: rotateX(270deg);
    }
    #b {
      transform: rotateX(90deg);
    }
    #l {
      position: relative;
      top: 180px;
      left: -60px;
      transform: rotateY(270deg);
    }
    #r {
      position: relative;
      top: -180px;
      left: 60px;
      transform: rotateY(90deg);
    }
  </style>
</head>

<body>
  <div>
    <br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br>
    <div id="container">
      <div id="l">
        <h1>left</h1>
      </div>
      <div id="t">
        <h1>top</h1>
      </div>
      <div id="b">
        <h1>bottom</h1>
      </div>
      <div id="r">
        <h1>right</h1>
      </div>
    </div>
    <br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br>
  </div>
</body>

</html>

Question 2

My solution was that I reset the vanishing-point every time the user scrolls.

$(window).scroll(function() {
    var scrollLocation = $(document).scrollTop();   
    var vanishingPoint = scrollLocation + window.innerHeight / 2;
    $("#wrapper").css('-webkit-perspective-origin', ' 50% ' + vanishingPoint + 'px');
})