This is easily done by position the mouse cursor onto the form using SetCursorPos, then using mouse_event to fake a mouse click.
// click in upper-left corner, 50 pixels inward
SetCursorPos (Form1.Left+50, Form1.Top+50);
mouse_event (MOUSEEVENTF_LEFTDOWN, 0,0,0,0);
mouse_event (MOUSEEVENTF_LEFTUP, 0,0,0,0);