Hi Rich, take the grips off the frame, put in a Tupperware bowl with lid, also place a small cup/shot glass of water in the center of the bowl, careful not to spill ....
.. you don't want water and grips to touch!! seal the bowl with all inside, and check twice a day. If the grips are still undersized, put back in bowl, replace the lid, and wait a day or two longer?... Sooner or later the artificial environment will hydrate the wood to a higher that normal level, but once in the air, they will assume whatever winter, or summer, humidity that is normal...
.. good luck, til...lat'r......GT