Can putting items with high heat capacity smooth out heat changes in Sous Vide? So was recently thinking about the beer cooler sous vide method and had a thought:

While heating the water to put in the beer cooler, if you were to place an object with a high heat capacity (e.g. a ceramic coffee cup) in the water, heat both to the desired temperature and then place them in the beer cooler, would that help keep the water at a more constant temperature?

In other words, since you are replacing some of the water with a material at a higher heat capacity at the same temperature that would in turn keep the rest of the water warmer for a longer period, correct?
Water has one of the highest heat capacities available:

http://en.wikipedia.org/wiki/Heat_capacity#Table_of_specific_heat_capacities

Your ceramic is not going to hold nearly as much heat as the water bath itself.

If you are finding that your bath is cooling too quickly then you are better off investigating your cooler.