You could mount ring style towel holders on the ceiling and thread the fabric through.
Or you could mount heavy plant hooks (like cup hooks) on the ceiling at the four corners of the bed, then suspend a pvc pipe frame (square). Drape the fabric over it.
If you think you would like to change the fabric often, just mount the hooks and buy the round clamp style drapery hooks to attach the the fabric. The hooks can be easily removed and replaced on new fabric.