I don't know if I understand you right (my English is not perfect), but when you mean, that using Bitcoin could prevent this from being illegal: I don't think so. The problem is not the amount of payment or the type of payment, but that it is a sales contract (at least in Germany, every sale would be made via a contract, if explicitly written or not -- also a handshake could be seen as contract). And the law just says, how any sale contract must be made ... There must be a good visible button that clearly states the intention: "Buy with costs" or something similar. The customer must be very clearly informed about the sale and the fact that he is making a sale now. Your demo informs afterwards in a rather weird way. Just giving a link and say "read further" or similar would be accounted to be a fraud, I guess. I am also not sure that having a different text would be enough.
I am no lawyer, but one remedy could be to have some kind of "frame contract" where you buy an amount of readings in advance -- and the readings afterwards could be accounted for with such a system. But such a frame contract would of course counter your ease of use goal -- and of course would bind the customers what would counter your goal to lower barriers.
