Implementing abap OO in UWL

I'm trying to realize a self-defined workflow using wd4a as the user dialog.

But I wanna compose ABAP OO into workflow now, for using ABAP OO can help to clarify the workflow logic.

So how to implement abap OO in UWL?

Before I defined a task and assign it to an application using SWFVISU, and the program logic was implemented in the called wd4a application.

How can I use abap OO in wd4a application?