1)
umm I mean you do have an 8x8 grid (8 bits each row) and you could have pieces make up bits being on or off and make a 8 letter phrase (each row being it's own letter).
(Ascii Wikipedia for your reference - https://en.wikipedia.org/wiki/ASCII#ASCII_printable_code_cha...)
2)
Maybe you could also do something like the Where Am I Game?
example:
I stay one night in Denver; four nights in San Francisco; And one night in Washington DC;
Where am I?
1 Denver = D 4 SanFrancisco = F 1 WashingtonDC = W
(DFW) -> Dallas
So you could do something like playing a chess game and for every attempted move (like player 1 moves a Rook but keeps his hand on it and taps the board thinking about the move and then places it down means the letter 'o').
3)
There was also a movie with Bruce Willis (or The Rock Johnson. I always get them confused). Where the main guy tries to escape from a space prison. There was one scene where they communicated over a chess game by only talking when there hand was on the queen. Any word spoken while on the queen was then concatenated to a sentance to convey what they were really talking about.
Then arrange an instant messenger software to interface with the chess playing AI so you type up the message and it plays the move using the right length of time for each letter
Then you can translate in real time, or save the moves with times and convert the whole message at once.
Play multiple games to send longer messages...
Then you could use a different shifting cypher for each colour to fool breaking the code, or even implement some kind of one time pad.
Example here:http://www.chessbymail.com/score.htm