Actually, this will be easier......

You need to make two parallelogram frames (to create an offset).. The height needs to be about 9" (one wing chord apart) the length needs to be a bit longer than the chord of the wing. The two frames can be held together by dowels at a distance just over the width of the fuse.
This way, you can slide the frame over the bottom wing and hold it on with elastic bands through the dowels. The top wing can also be held on with bands.

This way, you can fly as either a bipe or mono. You can also switch the frame around for +ve or -ve offset.

BTW, just an idea, I've never tried it....