Late answer – I also added this answer on the other Q as addition to my answer.
Possible solution
Your best bet would be to use
- A Plugin that makes use of Custom Post Types, then use something like the RW_Meta_Box class library to add custom fields for seat reservation to the event.
- Use a DB-option to store all seat numbers (Use the Transients API to clear the entry after the event has expired).
- Then retrieve the custom field with your seat numbers option during attendee registration and offer only the available seats.