Found the answer thanks to Rob Wunderlich.
In the search string you can use an expression with the field name to make an exact text value selection.
For the list box in the example above you can do the following...
<head>
<script language="javascript">
var userNameListBox= qva.GetQvObject("LB01", function () {
});
function selectUser() {
// the name of the field associated with the list box.
var fieldName = "UserName";
// where to get the name of the user to select.
var userName = document.getElementById("userNameInput").value;
// create the search string for qlikview to select.
// the expression should look like this "=[UserName] = 'John Al'"
// use "=" to indicate the search string is an expression
// use ' single qoutes to wrap the value
// if you want select multiple values you can use an "OR" like so "=[UserName] = 'John Al' or [UserName] = ''John Ala"
var values = ["=[fieldName] = '" + userName + "' "];
// qlikview ajax api to do the select text.
userNameListBox.QvaPublic.Data.SelectTexts(values);
}
</script>
<body>
<input id='userNameInput' type='text' value='John Al'/>
<input id='selectButton' type='button' value='select' onclick='selectUser();'/>
</body>
