I believe you should be trying to create a negative pressue inside the case so that heat will be drawn out; therefore even if you do not have an intake fan in the front, your single case fan in the rear should be an exhaust fan. With a little cable management (zip strips) your rear exhaust fan should be able to draw air from the whatever vents the case has, across the hot components, and blow the heat out the back.
Especially if your case doesn't have a funnel to the side of the case to let that CPU fan blow out, you really need that exhaust fan to do something with the heat the CPU fan is blowing out into the interior of the case.