Actually all sorts of things disagree with you. Firstly according to thematics a circle is something any mortal can do at any time if they have sufficient knowledge and a little blood. Secondly mortals can actually perform rituals without having the ritual power. It's called "Common Ritual" and it's a trapping Lore.
Common rituals, yes.
What he gets up to in his most recent appearance? No. Making the sorts of devices as he does with Bob's help--like the ghost radio--are hardly what I'd call "common".
And again this bothers me, because you are forcing a severe mechanical handicap, with absolutely no mechanical upside. If you offer this solution to a character who proposes the "Wild talent" character concept, they will turn you down and find something else to play. Then you will never have a "Wild talent" character, which is a pity because they can be lots of fun.
Hate to say it, but sometimes not every character concept works out. Some things just don't work in any given system.
Of course, there's nothing stopping me or any other player from coming up with a custom power for this purpose--probably something 1 refresh that they could upgrade to one of the dedicated spellcasting powers. Something like, "Once a scene, you can use your innate talents for a +2 bonus to block and maneuver actions."
Edit: Actually, that sounds like a good idea. I think I'll write something up for the Custom Powers thread later.
I just don't see the logic in having a character concept that's based around magic and not having them take some kind of magic power. The setting's pretty clear that if you have magic, that costs something in the way of humanity/free will/whatever you want to call it, represented by Refresh.
Given that, with the right circumstances, you can 'buy' a power for a scene just from spending fate points and that channeling less it's focus item slots is about refresh, I see nothing wrong with someone sufficiently unskilled in magic that they can't reliably call up meaningful amounts of power having their unreliable access to magic represented as a few aspects that the occasionally invoke for trivial spells.
True, but I got the sense from that write-up that temporary powers were meant to be along the lines of "You grab Mjolnir for a scene" or "The Demon lets you use a little bit of his juice for a while," not something that's supposed to be an inborn ability of the character.
I mean, under that logic, you could have a "pure mortal" wizard or sorcerer who just spends 3 fate points every time he wants to use Evocation for a scene--but otherwise keeps the +2 refresh bonus.