Steam, as noted above, is a BAD idea ... it will condense on the wood ... you may as well open the humidor and pour a cup of water in, shake well and pour out the excess as put in a steaming container ...
Oh, and btw ... Slim is correct in saying it isn't even necessary to take the trouble to make it distilled water in the container ... as he acurately points out, the solids will not be evaporating from regular water ... distilled water, as a point of clear fact, IS nothing more than condensed steam, however fancy the process was that generated it ...