API for Creating Window Inside Flight Simulator X

Basically I need code that creates Dialogs inside Flight Simulator X. The code would be a part of my module DLL (started from flight simulator). The dialogs are must be sticky to Flight Simulator window, visible in Full Screen Mode, and must keep the focus of Flight Simulator Window (When clicked). However, the dialogs can be not movable, not resizable, and have only client area (I’m going to build own Graphical UI). Using of additional API like FSUIPC is not allowed. The code must be stable, readable and easy to adjust. Knowledge of SimConnect API and Win32 API are must.