by Jamie Kramer.
If anyone knows a non-development solution to this I would be interested to hear about that as well.
In the past we have customized the signup page for our clients to build some logic in like what you are suggesting. We used javascript and jquery to add conditional fields with some logic, and auto-complete dropdown selectors. We also added server side validation in PHP. This did require some changes to Moodle's code.
To your question, there is not a way to do what you want, built into Moodle.