客户化插件开发的问题

案例地址：http://club.kisdee.com/home.php?mod=space&uid=421257&do=blog&id=118403

我想将以下方法改成有参数返回，那该怎么接收该返回值呢？
public void WriteString(string data)
{
this.Dispatcher.BeginInvoke(new Action(() =>
{
if (this._txtDsp != null)
{
this._txtDsp.Text = data;
this.Proxy.FireCustomEvent(new CustomEventArgs("", "Success", "{message:'WriteString() Success!'}"));
}
else
{
this.Proxy.FireCustomEvent(new CustomEventArgs("", "Error", "{message:'WriteString() Error, component uninitilization!'}"));
}
}));
}