如何在flexigrid输入框中制作rpoption而不是下拉？

Question

    $("#flex1").flexigrid(
    {
        url: 'http://xyz.com', 
        dataType: 'json',

        buttons : [
            {name:'Delete', 
            bclass: 'delete', 
            onpress: deleteitem},
            {name:'Add New Manufacturer', 
            bclass: 'add', 
            onpress: additem}
        ],
        searchitems : [
            {display: 'Manufacturer', 
             name : 'manufacturer_name', 
             isdefault:true},
            ],
        sortname: "mid",
        sortorder: "asc",
        usepager: true,
        title: '<?=$this->pageHeading?>',
        useRp: true,
        rpOptions: ['20','30','40','10'],
        rp: $("#rp").val(),
        showTableToggleBtn: true,
        singleSelect : true,
        height: 265,
        width: 1000,
        autowidth:false
    }
    ); 

在Flexigrid中，rp选项通常是下拉列表，我们如上所述定义..如何将它更改为输入框？