Layers are not embedded in BGRAVirtualScreen.
To do what you want to do, you just need to define the OnRedraw event of the BGRAVirtualScreen (in the event tab, double-click on this event).
In the method, draw the layers on the Bitmap :
Layers.Draw(Bitmap,0,0);
Then, when you modify your layers, in order to reflect the changes on the form, call BGRAVirtualScreen.RedrawBitmap.