Working example:
{ name: "Id_ListaMultiple",
  index:"Id_ListaMultiple",editable:true,edittype:"custom",editoptions:{custom_element:multiCheckElem,
  custom_value:multiCheckVal,list:"2:Reposición;1:Solicitud Inicial"}},
function multiCheckElem(values, optio) {
    var id = optio.id;
    var ctl = '<div id="'+ id + '" class="checklist">';
    var ckboxAry = optio.list.split(';');
    var aValues = [];
    if (values && values.length)
    {
        aValues = values.split(",");
    }
    for (var i = 0; i < ckboxAry.length; i++)
    {
        var item = ckboxAry[i].split(':');
        ctl += '<input type="checkbox" ';
        if (aValues.indexOf(item[0]) != -1)
        {
            ctl += 'checked="checked" ';
        }
        ctl += 'value="' + item[0] + '"> ' + item[1] + '</input><br/>';
    }
    return ctl + '</div>';
}
function multiCheckVal(elem, action, val) {
    var items = '';
    if (action == 'get') // submitted
    {
        $("input[type=checkbox]:checked", elem).each(function (i, e)
        {
            if (items) items += ","
            items += e.value;
        });
    }
    else // launched
    {
    }
    return items;
}
Regards Henry