You need to make the real world experience even more worth it (I think it already is).

Yeah, the reactionary "oh no drinking might happen" will manifest, but tailgating is something that fan culture centers around and emerges organically from. Moving it from parking lot to parking lot to strip of grass by the admin building hasn't cut it...and the events near the stadium are too close. Tradition could be created with art, with pageantry, with earlier events, whatever.

Make Game Day something to be part of, to arrive earlier or leave later for, which helps with congestion and other things that impact attendance negatively.