I just read an internet discussion where potters were talking about reconstituting dried clay and some suggestions were offered for ways to wedge the clay that were a little less taxing physically.  One person suggested getting students to do it as part of their learning which is a great idea if you happen to have students!  

For the rest of us, my method of choice is to save my scraps from slab building (I use my clay fresh from the box and nicely pre-wedged for the slabs), in a 1 or 2 litre plastic case with a tight lid.  I spray my scraps with a little water as I add them to keep them nice and moist.  When I have a case of scraps, I switch and coil build until I use my scraps up, wedging the coils by rolling them out, folding them and re-rolling them a couple of times.  I spray them with water as I go which gives me nice soft coils to work with.

This is also a great way to 'wedge' clay and can be used for large amounts of it, depending on how strong you are http://www.youtube.com/watch?v=HApNjUnI9U4