How to send variable with plupload

Question

I am using plupload to upload multi-able files and i need to send variable with file url (mgr.upload.release.php) this variable i write it on input text with (cont_id) id before i upload files but this variable dose not reach to file why?

$j("#uploader").pluploadQueue({
    // General settings
    runtimes : 'html5,flash,silverlight,html4',
    url : "mgr.upload.release.php",

    chunk_size : '1mb',
    rename : true,
    dragdrop: true,

    filters : {
        // Maximum file size
        max_file_size : '100mb',
        // Specify what files to browse for
        mime_types: [
            {title : "Image files", extensions : "jpg,pdf,png"},
            {title : "Video File", extensions : "mp4,ogv,avi,mov,flv,3gp"},
            {title : "Zip files", extensions : "zip"}
        ]
    },

    // Resize images on clientside if we can
    resize: {
        width : 200,
        height : 200,
        quality : 90,
        crop: true // crop to exact dimensions
    },

    multipart_params : {
    "cont_id" : $j('#cont_id').val(),
    "name2"   : "name2"
},



    flash_swf_url : '../plupload-2.3.1/js/Moxie.swf',
silverlight_xap_url : '../plupload-2.3.1/js/Moxie.xap'
});