Not sure if this applies to conversions, but what I do know is that the ATPL courses, even via distance learning still require some classroom study time. I don't think you could just take the exams without meeting this requirement? Unless of course it is slightly different with conversions?
If you end up on a course, the FTO will have their preferred material which is usually included in the course cost. A few providers do have multimedia only courses with no books so I suspect you could just get the CD's and learn from them.
I think your best bet is to have a read of LASORS. Hope this helps!