As long as you are inserting one record at a time it can be done with the existing MySQLi Server behaviors.
You insert into the registrants table and save the ID in the session. Then go to the insert riders table and insert riders with the saved value from the session as the registrantID. Then set it to redirect to itself and show a table of existing registrants on the page with a done button that takes them back to their dashboard. You wouldn't need the BETA.
The BETA might be worth using since it would help you create the insert pages and tables. Since you can test everything locally first I wouldn't worry too much about using the beta on a live site. If you do have errors it would be in Dreamweaver or in getting the pages to work in the first place and then you could just choose not to upload them to the live site until they are working properly.
So... I'd personally use the beta, but you don't have to in order to get something like this working. A premier support ticket might be your best bet. Then I'd use the BETA and show you how I would do it.
I'd run the data assist wizard for both tables and then join the two with framework builder plugins and add the session variable relationships nad probably blow your mind a bit on how quickly and easily it could be done.