execCommand("insertHTML", ...) in Internet Explorer

I'm building a wysiwyg-editor with an editable iframe using document.execCommand(). Now i need to use the "insertHTML" command which works perfectly in Chrome and Firefox but of course it doesn't work in Internet Explorer:

function run() {
  document.getElementById("target").focus();
  document.execCommand("insertHTML", false, "<b>ins</b>");
}

<div contenteditable id="target">contenteditable</div>
<button onclick="run()">contenteditable.focus() + document.execCommand("insertHTML", false, "&lt;b>ins&lt;/b>")</button>

What is the standard solution to this problem? It's okay if it only works in IE8 but IE7-support would be nice too.