the best way is to just engage for awhile and ask them to optin. Much better results. Trust me. I actually did another test literally a few weeks ago to prove this out again.
Ok I have not looked at the thing for brands yet so not sure how you can manipulate it however.Are you kidding me? Linking a Facebook Ad campaign to a custom HTML landing tab was the best thing about Facebook. Now that we can't do that anymore, fuck it. Who has the time to engage people over a long period of time for a fucking opt-in?