I once bought a nice wooden travel Chess set where I actually did that. The chess board there was split as two 4x8 areas on both sides of the box the pieces were in, and the hinges would open the box such that these two halves would touch to form the usual 8x8.
So what I did is remove the hinges, and supplied a stick that had the width of a square to fit in between the two halves, to form the River. And then put pieces on the corners f the squares, rather than in the center.
Okay so let's say someone wanted to create a dual Western and Chinese Chess board, like how there are dual Chess and Checkers boards. Would that even be possible? The Western board has 8x8 squares, while the Chinese has 8x9, but would a 8x8 Chinese Chess game still be playable? Or is there perhaps another way to make them compatible?