Yeh, the hub would be completely different, so it wouldn't fit into the forks properly and would also have a freehub (I'm guessing from the 27's) sticking out the side. The hassle it causes is not worth the €60 or so it would cost for two new (low grade) wheels. Unless you find a handy solution, which I don't think there is. You could just change the hub, and reuse the rest of the wheel, but I don't think it's worth the hassle!

And I always try save the pennies on my builds, so I wouldn't normally tell people to buy their way out of a problem!