Well, all I can think of is sending EM_SETSCROLLPOS into your edit control.
See
EM_SETSCROLLPOS Message() for details.
Sending a message into a control can be done in 2 ways:
code:
PlusWnd.SendControlMessage(ControlID,Message /* in your case WM_SETSCROLLPOS */ ,wParam,lParam);
or
code:
Interop.Call("User32.dll","SendMessageW",PlusWnd.GetControlHancle(ControlID),EM_SETSCROLLPOS,wParam,lParam