Dynamic number of form inputs

How do I set a form up so that the number of input fields is dynamic, based on an initial multiselect input box? Users will first select which sections they want to include in a report using a multi-select dropdown box. Then, for each section, they can choose one or more components to be included in that section. So for example if they choose 2 sections, then I need two additional multiselect dropdown boxes, one for each section. If they choose 4 sections, then I need four more multiselect boxes to appear. The number of sections could in theory be infinite, but in reality most reports will have no more than 5 or 6 sections. I could hard code 6 multiselect boxes that appear as needed, but if someone ever chose more than that I would be out of luck. Any ideas? Is there a way to just keep spawning new inputs on a dynamic basis?

Thanks, that could work. I think I found another way to accept input to avoid that need, which keeps things a bit simpler anyway. Appreciate the help!.