Чтобы выполнить клик и переместить курсор за пределы формы через код:
[DllImport("user32.dll")]
static extern void mouse_event(int flags, int dX, int dY, int buttons, int extraInfo);
#region mouseConstants
const int MOUSE_MOVE = 0x00000001;
const int MOUSE_LEFTDOWN = 0x00000002;
const int MOUSE_LEFTUP = 0x00000004;
const int MOUSE_RIGHTDOWN = 0x00000008;
const int MOUSE_RIGHTUP = 0x00000010;
const int MOUSE_MIDDLEDOWN = 0x00000020;
const int MOUSE_MIDDLEUP = 0x00000040;
const int MOUSE_WHEEL = 0x00000800;
const int MOUSE_ABSOLUTE = 0x00008000;
#endregion
private void performClick(int posX, int posY)
{
Cursor.Position = new Point(posX, posY); // to move the cursor at desired position
mouse_event(MOUSE_LEFTDOWN, 0, 0, 0, 0); // to perform left mouse down
mouse_event(MOUSE_LEFTUP, 0, 0, 0, 0); // to perform left mouse up
}