Would Onsite Testing be an idea? Setting up field laboratories like we have seen for anti doping testing at sporting ideas might be something to help out with quick test.
Polymerase Chain Reaction Testing is what is currently used for testing for COVID-19. Maybe testing will become more widespread and readily available, but it might be an idea for events as an added benefit.
After taking a nasal and throat swab, and the test is securely transported to the lab, the testing itself takes about an hour. What i don't know is how big a laboratory would need to be and how many samples they could process, but it might be an option for people coming to the event.
There are definitely both advantages and disadvantages of this, however might be something that clients would like to test out, and potentially might make councils and governments more happy to have you run your event...