title: Knockout.js - How to create a custom bindingHandler similar to 'with'
body: <p>I'd like to make a custom bindingHandler, something like <code>data-bind="withSmartForm: formModel"</code>. </p>
  
  <p>But despite all the other functionality I want it to behave like <code>with</code>, so the current context changes to formModel, and I can access the subproperties like <code>data-bind="value: email"</code>.</p>
  
  <p>I know there are workarounds like always prefixing the subproperties with formModel, or put a <code>with: formModel</code> in a parent element, but as I will be using this pattern a lot I'd like to keep it as short as possible.</p>
  
  <p>In the following fiddle I'd like to merge the <code>with</code> and <code>withSmartForm</code> into one bindingHandler.</p>
  
  <p><a href="http://jsfiddle.net/k89Fg/1/" rel="nofollow">http://jsfiddle.net/k89Fg/1/</a></p>
  
  <p>Any ideas? Thanks!</p>
  
  <p><strong>Update: working example</strong></p>
  
  <p><a href="http://jsfiddle.net/k89Fg/4/" rel="nofollow">http://jsfiddle.net/k89Fg/4/</a> - thanks to Andrew Walters for the winning answer!</p>