I think you would find that even once you DO create custom user variables, your options are quite limited as far as tracking what the user actually answered in each question.
There is a system quizzing variable called cpQuizInfoAnswerChoice which records the user's chosen answer on a question, but this only shows you whether the user chose option A, B, or C etc. It doesn't show you the actual text from their answer. So in order to use this variable to provide some kind of personalised feedback, you would need to hard code your feedback Advanced Actions to show certain feedback on A, different feedback on B etc. The other thing to remember about this variable is that it will get updated after each and every quiz question. It doesn't get stored in an array or anything. So if you wanted to track the user's choices with this variable, you'd need to set up your own variables for each quiz question and write the value of cpQuizInfoAnswerChoice to those variables after each question.
Bottom line is that this would be quite complex to pull off, might not deliver the granularity of detail you really wanted anyway, and would be a bear to maintain after you built it.
