I've heard of people having some success warming the supers with heat
lamps before extracting, but this only works with mild cases of sugaring.
 
A more serious problem is that small quantities of honey crystals left
in the cells will act as seeds for rapid crystalization of the next crop.
You better make sure they do a very thorough cleaning or those will always
be troublesome frames that will need rapid extraction.  My bees have
been enthusiastic cleaners if I wait until cold weather to give them
wet supers above an inner cover.