Most of the hitch mount bike racks tilt or swing to allow access to the rear of the vehicle. The one I bought off ebay was a 1-1/4" so I bought an 1-1/4 to 2" adapter to fit my 2" receiver. One of the benefits of the adapter is that it moves the bikes about 4 inches further from the back of your vehicle. There are also models to that are longer to clear rear mounted spares.
There are tiltback racks like this
http://ep.yimg.com/ca/I/orsracksdirect_2070_346714
or swing out rack like this
Surco Swing Away Bike Racks
HTH
David