Can I add a booster fan to increase pressure?
What is it that you want? Flow or pressure. CFM is a measure of flow rate in cubic feet per minute. Pressure on the other hand is created by forcing more and more air into a confined volume which implies that the flow rate is decreased!

If it is simply more flow rate that you want through a certain sized volumetric space then use a larger fan on the ducting into the working space. You also may have the option to increase the rotational speed of the fan which will increase flow rate as well. 

Another option is to redo the input ducting in a Y arrangement and use two fans, one on each arm of the Y and have the air flow from each merge at the leg of the Y and into your working space.