I've been wondering how many believers you need to start a religion. If people managed to get Jedi Knight as a religion you wouldn't need too many people to found one.
I'm sure they exempted all churches from using psychoactive substances in their religious gatherings, so founding the Church of Psychonauts/The Order of the Great Blue Light would legally exempt members from taking whatever the fuck they wanted, depriving people of that right would be in violation of article 18 (Freedom of Belief and Religion) of the EU/worldwide human rights declaration. Naturally drugs would feature heavily in religious sacraments.
If they want to do silly things like
ban everything I say we should respond by rendering their ban meaningless, turning their own law against them. If they arrest people taking part in religious sacraments it would be a hate crime by the state. Mesoamerican tribes use psychoactive drugs lots during their rituals and in the US native Americans are exempt from certain drug laws. It's been proven that animals will take drugs without any human intervention (such as kangaroos eating the heads off poppies in Aus) so it can be argued that substance use is a natural drive and our religion brings us closer to nature as well as closer to an understanding of your individual identity. With enough backers, angry at the 'war on drugs' supporting this new religion we are essentially giving the message that if they close one legal loophole we will just find another, larger legal loophole and run with that.
Come to think of it, pastafarianism (giant spaghetti monster) has religious status, so getting it can't be that hard. There are churches in NYC that use a 2c-x compound as one of their sacraments with no police intervention.
EDIT:
Here's a guide, so who would be on board for starting a religion?