Add user custom select item to selectOneMenu

Question

I need to add a user custom select item to a select one menu, shown as last item below:

<p:selectOneMenu id="mail_house" value="#{projectDataService.mailer.mail_house}">
    <f:selectItem itemLabel="DOCUMATION" itemValue="DOCUMATION" />
    <f:selectItem itemLabel="NCA" itemValue="NCA_ACP" />
    <f:selectItem itemLabel="JS DIRECT" itemValue="JSPOD DIRECT" />
    <f:selectItem itemLabel="PLATINUM" itemValue="PLATINUMDIRECT" />
    // User customized entry as opposed to the available items.
    <f:selectItem itemLabel="OTHER" itemValue="COLLECT USER INPUT TEXT HERE" />
</p:selectOneMenu>

How can I achieve this?