This has been asked before and I don’t have a good solution for it. Maybe someone from the community has tackled this before and has an approach to share.
You could just use the actual chain select field. In the .csv file, after each Option the followup would be all the options that weren’t selected. Wouldn’t be too difficult if you knew all the options ahead of time.
Otherwise it’s doable, but would require a bit of customized coding. If you don’t feel comfortable with coding Ajax and PHP, I wouldn’t attempt it.