My suggestion would be that you call a ASA school and ask them which classes you can test out of. I think that you will find that the answer will vary by school and what you are attemptiing to accomplish. There is a fee to test through classes which covers materials and man hours.
Certainly the written exam for 101/103/104/105, etc. could be passed quite easlily by studying the books that coincide with the class. I don't remember any questions on the test that were not covered in the book, and with the exception of 105 Navigation the questions are mostly multiple choice and covered by reading and digesting the material in the book. The Nav test is a lot harder than the Nav test for a Captains licence.
You will probably find schools that will test you through 101/103 if you are taking 104 or 104/105 from them. In that way they can also see and test you on the actual boat handling part of the courses as well. Dingy sailing will not prepare you to dock a 30 something 12,000 pound boat, but most of the sailing skills and terms are easily transferable.
Some sailing schools will let you charter one of their boats after you have passed 101/103 and they are comfortable with your learning. Most charter bases want to see your sailing resume and 104 level before you charter. Even if you could test out of all the ratings you will have to prove your ability to a charter base. If they do not feel you have the skills, they will require a captain for the time you need to get up to speed which will increase the cost of the vacation and delay departure in some cases.
You can pass all the tests and still not have a clue of what to do when the **** hits the fan unless you have had enough experience to have some logical reactions. If you owned the charter boat would you want the charter company letting someone taking your investment out based on the fact that they read about it in a book?
However, I am convinced that in some cases the available credit on your Visa card is enough to get you a boat for a week with some charter companies. Good luck with your quest.