What I'm wondering is if it's possible with a high degree of success.
Yes. Just as it is also possible to have a high degree of success with winning the lottery. That is, if you buy 99.9999% of the ticket combinations. Not trying to be an ass with my answer, but without the underlying foundation you will likely have a rough go of it. Also I'm not sure what you consider "a high degree of success." Some people here consider anything above an average score "a high degree of success" for themselves. Are you looking at a composite in the 70's (about avg), 80's, 90's, 99%? You should be asking yourself the following:
1) Did you take Calc in HS and do well in it?
2) Do you have a good understanding of general biological principles (i.e. how a cell works, how the body functions, plants/animals, ecosystems, etc)?
3) Did you take any sort of advanced placement chemistry in HS?
4) How would you rate your reading comprehension/writing/verbal abilities?
5) Are you a quick learner?
If you answered yes and ranked yourself highly in the areas above, then you should have enough of a foundation to perform well on the PCAT. That is provided you put in a tremendous amount of time and effort required to understand the material. A Kaplan book (IMO a terrible choice BTW) or a course isn't going to teach you everything you need to know. It isn't a substitute to having the knowledge, it is a supplement to help refresh the skills lying in dormancy.
If you are exceedingly bright and put in a solid effort (multiple hours per day of studying material over a period of at least a few months) then yes I could see you hitting in the 80's and maybe even 90's. It's not that the material is that difficult, it is that there is a lot of it and not all of it is a stepwise mathematical/chemical problem where you can learn the steps and thus know how to do every similar problem thereafter. Some of it is knowledge based that no book/class can adequately prepare you for. The best those books can do is give you tactics on how to possibly work around not knowing the answer.
Best of luck.