How to bind a single property to a value with oDataModel?

I've had a look through the guides on binding, and I've tried a lot of things but I'm still struggling with this. The data service I'm calling returns this in the browser.

<feed xmlns="http://www.w3.org/2005/Atom" xmlns:m="http://schemas.microsoft.com/ado/2007/08/dataservices/metadata" xmlns:d="http://schemas.microsoft.com/ado/2007/08/dataservices" xml:base=" http:exampleurlfordataservice/zui5_purchase_order_srv/">    <id>         http:exampleurlfordataservice/zui5_purchase_order_srv/zui5_purchase_order_srv/UI5UserParameters    </id>    <title type="text">UI5UserParameters</title>    <updated>2014-01-27T13:11:17Z</updated>    <author>        <name/>    </author>    <link href="UI5UserParameters" rel="self" title="UI5UserParameters" />    <entry>        <id>            http:exampleurlfordataservice/zui5_purchase_order_srv/UI5UserParameters('USERNAME')        </id>        <title type="text">UI5UserParameters('USERNAME')</title>        <updated>2014-01-27T13:11:17Z</updated>        <category term="zui5_purchase_order_srv.Zui5UsrParm" scheme="http://schemas.microsoft.com/ado/2007/08/dataservices/scheme" />        <link href="UI5UserParameters('USERNAME')" rel="edit" title="Zui5UsrParm" />        <content type="application/xml">            <m:properties>                <d:Purgrp>BBB</d:Purgrp>                <d:Purorg>VICK</d:Purorg>                <d:Storloc/>                <d:Plant>ABDN</d:Plant>                <d:Username>USERNAME</d:Username>            </m:properties>        </content>    </entry></feed>

I'm trying to bind the username to a searchfield, and I just can't figure out how. I've tried bindProperty with several different parameters, as well as binding the value in the constructor, and everything just returns no errors, but no data either in the searchfield. Help would be greatly appreciated.