为asp.net webforms应用程序实现插件架构的最佳方法是什么？

We have a 3-tier web application written in ASP.Net Webforms where we will not be able to port it - recession really sucks! - to MVC. Our goal is to implement a plugin architecture. One way would be to use the App_Code folder. Are there any better alternatives?We have a 3-tier web application written in ASP