Yes, that's certainly possible, but it has all kinds of problems. Mercurians won't want to teach others Mercurian magic, for example, a master may not want to "trade" the teaching, because they don't want their apprentice to have the other master's virtues.
I wouldn't allow a virtue to be "purchased" from books, but I would bestow a virtue on an apprentice who read relentlessly on a particular subject to the exclusion of other stuff, perhaps...maybe.
One of the philosphical things I have a problem with, which is touched on in Apprentices, is the idea that good books are given to apprentices straight off. We have a Creo volume L6Q21. I'll give it to my apprentice to read while I'm reading something else. To us, as players and modern people used to have books lying about, it makes sense. Apprentices does indicate that books are precious and suggests that they shouldn't be given very freely.
While that is quite possible, having read through Apprentices I don't see a lot of wiggle room for transforming a Supernatural Virtue into the Gentle Gift. It would also make the Gentle Gift a virtue that a character must have, which is contradictory to the book. My underlying issue is that Apprentices seems to create more problems than it solves. If you Errata Gentle Gift and say it and perhaps it alone is innate, then why can't other virtues be innate?
What it amounts to is that Apprentices seems to create more problems than it solves. This is just my opinion based on playing Ars for a while and thinking through the apprentice process. It could be nothing but a paradigm conflict. Even if it is declared errata and fixed, I still have difficult time with the entire Virtue Flaw transmission process in general.