I haven't given it much thought, but you would probably have to do something involving a few things.
1. event.preventDefault on the List when something is clicked
2. Listen for clicks, get the clicked item, put in the selectedItems array of the list.
3. Check to see if item was already in selectedItems list, if so remove to deselect it
Like I said, I didn't give this much thought, especially on the event.preventDefault but that is where I would start. But there probably is a simpler solution out there.
See, I was overthinking what someone had already thought.
Thank you both