Custom redirect on successful booking submission

I need to redirect user to another page upon successful new Booking submission, and pass newly created booking_id as a parameter in this redirect (i.e. something like http://<site>/successful_login?booking_id=1182).

What parts of the plugin code should I be looking at to make this hack?
It looks to me like bookingsform.js supports response.redirect – but how do I make PHP return it?