Give this a try:
At the beginning of each turn, that player randomly selects a chess piece (we used tokens) and places it on the board at its normal position. When placing a piece that can go in multiple places, the player can select any appropriate square that has not yet been used (one white bishop, one black bishop, eight pawns, etc.). Then the player makes his move, using any of his pieces on the board except the one he just placed. The Queen and then the King are placed last.
Its really added a lot of fun to the centuries-old game. Do you build a defense for the eventual emergence of your King? Do you try to establish control over areas of the board or do you engage in a blood bath to eliminate pieces early? Do you try to set traps for key pieces, knowing they will eventually appear?
Just something to try. We've had so much fun with this we're seriously considering marketing it with a special board and pieces that are indistinguishable by touch.