Could you tie it into a pared down version of Rival chess? Since that program is already available for pawnstars, maybe a version that has the computer AI removed would be useful. Clicking on a button in the details section of the game would open a copy of this 'lite' version of Rival chess with the FEN position of the board already loaded in. All that would be required is that the person download this reduced version of the Rival Chess.
I just thought it might save you some time, anyway. I guess Rival would have to be configured as a browser plug-in, but that doesn't seem like it would be that difficult.