Okay, so this is why this extension does not work 100%.
It allows an Element to be blank, but assigns a value to it, so therefore, your selection will always have a value to it.
<select name="attributes[10]" class="form-control " id="attributes10" data-placeholder=""> <-- Where do I set this in the Extension?
<option value="101"></option> <-- How can I set this to "selected disabled"
<option value="102">Sales Rep 1</option>
<option value="103">Sales Rep 2</option>
<option value="104">Sales Rep 3</option>
<option value="105">Sales Rep 4</option>
<option value="106">Sales Rep 5</option>
<option value="107">Sales Rep 6</option>
<option value="108">Sales Rep 7</option>
<option value="109">Sales Rep 8</option>
<option value="110">Sales Rep 9</option>
<option value="111">Sales Rep 10</option>
<option value="112">Not applicable</option>
</select>
Regards
Chris