Seems like this would make more sense to have a page type that would contain different booking events. That way you can have a main event, and choose the events(which in this case could be the different registrations or days). May be more setup for the end user, but also would be out of the box functionality. So for each main event(new page type) you could select the events to allow sign up for, Maybe through a uniselector or something along those lines.
The only downside is that the end user then has to create the registrations after the event and attach them. Plus your transformations will need to handle multiple (booking events)registrations underneath, so it may make sense to take what you have and see if you can figure it out. Just throwing out an alternative for a last resort.
You could always clone the kentico webpart for event registration and customize it to check those properties and use that approach if you can't figure out the macro.