Is it possible to use 5 motors on an EV3 brick?
A sensor port can't directly output to a motor. The sensor drivers can't provide enough power to supply a motor.
You have a couple options:  


Daisy-chain two EV3s together. The first can control the sensors and
motors of the second.
Use an electronic motor multiplexer. EDIT: It should be noted that this requires an external power supply, which will increase the cost and complexity of your project.  
Depending on your project, you might be able to make do with only 4 motors. See this response for driving multiple outputs with a single motor.