I'm currently watching season 4 of Angel for like the 50th time (ok, that's probably a slight exaggeration) and I can't help noticing that between the end of season 3 and throughout season 4, there are a lot of attempts at dark magics made (some unsuccessful, some successful with hefty complications). The "ritual casters" (to use the 13th Age term) range from Wesley (training as a Watcher), Fred (generally book smart), Lorne (contacts), to Angel himself. None of these characters could be considered witches/warlocks. When magic is used on Buffy, it's usually done by Willow (the vast majority), Tara, or Amy (all witches), and occasionally Giles or Dawn (same deal as with the Angel characters - not witches).
To further the analogy, the witches on Buffy would be spellcasting classes if you had to force them into 13th Age (or at least an RPG with a ritual system reminiscent of the one in 13th Age). But the non-casters get to do magic too!
See where I'm going with this? Everyone's gotta start somewhere, right? Before he cast his first spell, a Wizard is not yet a Wizard. For those who want magic to be more accessible in their worlds, I've been thinking about an optional houserule.
So normally Clerics and Wizards can simply perform a ritual, expending an appropriate Daily spell in doing so. Other spellcasters (usually Bards and Sorcerers, in the core book) can pick up the Ritual Caster feat and do the same thing. The point of rituals in the game is to allow the magic-user to manipulate the magical energies in improvised ways to weave together a unique effect. They can bend the magics to their will.
Non-spellcasters don't have Daily spells to expend, though. But there's a workaround for that. Ultimately, here's how I would envision an un-trained practitioner going about casting a ritual in my games. First of all, the skill check would likely be a straight-up Int check. Depending on the complexity of the ritual, it might be penalized, too, but that can be negated with extra preparation. Ah, preparation. That's the big difference, isn't it? A non-caster would have to research the potential ritual, not having the training or intuition to bend magic to their will on their own. It's more like following a recipe for them. Perhaps they'll need to gather more ingredients, components, or foci as well. All of this will take more time. Without a magical background, the skill check is also less likely to succeed, meaning that the spell has a higher chance of "going wrong" (which could simply mean complications, as that's more interest than straight-up failure). But then there's the Daily spell wrinkle. I say no problem! Just have them spend a recovery instead. Perhaps they're draining their energy, unused to their body being used as a magical conduit, straining their mind, or using a form of blood-magic. There are a lot of ways to justify the use of a recovery. Perhaps a full caster can opt into that as well, but they'd have to go through the same process as a non-caster; without using a specific spell as a base to build upon, there would need to be research, and complications might be more likely.
See, just because you're a "martial" character doesn't mean you have to be barred from dabbling in magic from time to time.