Agreed with other posts in this thread, the best way is to create a landing page for the event and have people fill it in there (or fill it in yourself afterwards - painfully manual, Hubspot).
Note of warning from someone who learned from terrible experience:
If you create a landing page for an event and you want people to sign in from one particular device, make sure the form you use has cookies disabled. If cookies are checked, it will merge all of your contacts from one device into one contact. I almost cried. Go to the form settings to do that.