Hack 12306 page to get hidden select bed option.
Open Chrome and install woyaoxiapu.crx (Chrome extension)
Download the extension file from the website and save it to your computer. Click the wrench icon on the browser toolbar. Select Tools > Extensions. Locate the extension file on your computer and drag the file onto the Extensions page. Review the list of permissions in the dialog that appears. If you would like to proceed, click Install.
Follow common steps, you can see “随机” in “乘车人信息”, selete bed you want from it.
thanks to: vayco ( http://weibo.com/136088901 )
修改12306订票网站，增加了选择铺位的功能
打开chorme浏览器，安装woyaoxiapu.crx (Chrome插件)
从网站下载扩展程序文件并保存到您的计算机中。 点击浏览器工具栏上的扳手图标。 选择工具 > 扩展程序。 在计算机中找到扩展程序文件并将其拖动到“扩展程序”页。 在显示的对话框中查看权限列表。如果您想继续，请点击安装。
正常流程点击预订后，在乘车人信息中出现“随机”字样，打开下拉菜单选择铺位。
特别致谢: vayco ( http://weibo.com/136088901 )