You can do well on the PCAT without taking all of the recommended coursework. However, it hinges on how well you know the other material. For example, there are many students who have taken General Chemistry, so they have seen the concepts, but they purged the material after the exam.
I'm a hardcore advocate of not taking the PCAT until after you've taken all of the classes. However, there are people who have been successful without it. Your performance on the exam is intrinsic upon how well you actually retain the material that you've learned from the classes that you have taken and how well you can traipse through the minefield of questions from which you haven't learned the material. It's definitely possible, but I would never advocate doing that.
My thought process is: Would you take an exam which is rather important to your acceptance to a program without studying for 20% of the material? If the answer is Yes, go for it. If the answer is No, I'd wait until I had finished the classes.
Good luck!