Not sure how small your Timbuk2 bag is. Mine is the "Freestyle" model designed for a netbook or an iPad to fit in an sleeve inside the bag. I don't believe the company makes a smaller bag. If that's the bag you have, the Apple Wireless Keyboard fits fine with room to spare. In fact, I carry my AWK in an Origami Workstation case in the Timbuk2 bag and have room for lots of other stuff (power cube, cable, headphones, etc.).
If you're still concerned, keep in mind that the AWK is about two inches wider than the length of the iPad. So if you have a bag at least 2+ inches wider than the iPad you should be fine.