I'd like to hide the corresponding button when an input value is empty or has a value="n/a".

In the following example, the input box "boat" is corresponding with the button "button_boat", and the input box "car" with the button "button_car", and the input box "dog" with the button "button_dog".

Note: you cannot change the properties of the input element with type="text".

HTML Code:
  <div>
    <form action="">
      <fieldset>
        <input type="text" name="boat" id="boat" disabled="disabled" value="n/a">
        <input type="text" name="car" id="car" disabled="disabled" value="2">
        <input type="text" name="dog" id="dog" disabled="disabled" value="">
      </fieldset>
    </form>
  </div>

  <div>
    <div id="button_boat"><input type="button" value="Boat"/></div>
    <div id="button_car"><input type="button" value="Car"/></div>
    <div id="button_dog"><input type="button" value="Dog"/></div>
  </div>
Without script the output will look like this:
hide_button_when_input_value_is_empty_before.gif

With script the output will look like this:
hide_button_when_input_value_is_empty_1.gif

Anyone know a Javascript that can do this?