Sub-attributes? Making attributes of attributes appear based on which you select?

I was wondering whether it is possible to create sub-attributes, that change dynamically based on what your parent attribute selection was.

For example, I have a product, which is a half-day conference registration pass. The conference goes three days, I need a morning and afternoon option for each day, except Monday, which will have no morning session, and Wednesday, which will have no afternnoon session.

I was envisioning a set of radio buttons that appear based on which Day attribute option you select, so if the user picked Monday from the Day attribute drop down menu, they would only be given the afternoon radio option by default, but if they picked Tuesday, they would have both the morning and afternoon radio buttons to pick from.

Not sure if this is possible, my fall back position will be to make each half day it's own attribute option, since there would only be 5 in this situation, but I was thinking the dynamic way would be slicker...