Here's a spoiler for a book not covered by the game. I'll use the spoiler tag, and if you don't want to know what happens in one of the later two books (Turn Coat or Changes - I won't say which) then don't move your mouse over the blacked out stuff:
You don't need a circle for a magic circle. It's true - if you don't have time to make a circle you can mentally picture one and it can work. It won't be as good as a real one, but all magic comes from the mind and soul with the tools there to help the wizard focus. If you are in dire straights you can skip those tools and do it with raw intent. In game terms I'd say it involves taking mental stress or consequences to do it this way - say maybe a ward strength linked to the level of mental consequence you're taking.
Yes, that does seem to go again the rules of the game, but Butcher isn't constrained by the game's magic system. It was cool, "this has to work" move and Dresden went with it.
Richard
Something similar occurs in Fool Moon:
Harry uses the circle formed by spinning his mother's silver pentacle around his head on the chain in order to cast a spell in the showdown with the Loup Garou