There is actually but it involves some math.
Change the settings from Constant Quality to Variable bit rate. If you are doing this, I would strongly recommend you do a 2-pass encode as well, which will double your encoding time, but give you a much better encode. You can also set turbo first pass if you like which has a very small degrade of quality and shortens your first pass by about 50%. If you are looking to have every encode less than 4GB I would say a bit rate around 3500 should get you between 2GB-4GB encodes depending on the length of the movie.