New purchase and trade in
Will the Apple Store transfer the data on a old iMac to a new Mac at purchase
iMac 27″
My understanding is that they can do this when you purchase a new Mac in the store (or pick up at the store).
However, you may need to make a Genius Bar appointment in advance. Call the store and ask them about it.
And of course you would have to bring in your old iMac.