I have seen it done before,but it has required a large amount of fucking around trying to find brakes with the most pad adjustement, and then some dremel modification as well. Helps heaps if you have the old school slotted dropouts on your frame.
But really why? I'm presumming you'd want it as a commuter, but with 27" wheels you're bacically limited to 1 1/4 or 1 3/8 tyres in a couple of cheap models. You'd have much better tyre choice in 26": just run some 1" Tom Slicks if you want fast wheels.