Howdy Aisling,
It sounds like this WooCommerce plugin might be what you are looking for: http://www.woothemes.com/products/woocommerce-checkout-add-ons/
I have not personally used it so I can not say for sure, but give it a look. Basically if a users adds an item to their cart, like a ticket to a 4 session event, it allows you to have extra options added upon checkout. It looks to me like it might even allow you to setup 4 different required radio fields with 9 options each, and from the soudns of it that is exactly what you need. This would all happen at checkout.
Again I have not run that plugin myself. Based on everything I have read it should work perfectly with WooTickets, our plugin that allows you to easily add tickets to event and for a user to add those ticket products to their cart.
Does that answer your question? Please let me know if you have any followups, or if that settles it for you. Cheers!
– Brook