We have a small, diehard fan base ... the South Ward and a few thousand ..., nothing we can do about other people not showing up. That's the team's responsibility.
IMO, existing fans can try to bring old fans back, or potential new fans, on an individual basis. There are some STs in 101 owned by ESC, to keep the section sold out, which AFAIK are sold each game to ESC members and perhaps guests. 133 has empty seats, but IDK how they are marketed.
There are some things that RB does. NAWT: Never A Wasted Ticket gives ST holders the chance to switch game tickets to another match, at no extra charge.
There are also emails to STs offering deals on extra tickets.
I would also expect that RB sends mass emails to an existing database of those who have previously purchased tickets, whether single-game or ST. I get emails regularly from other MLS clubs, from whom I have previously bought tickets as an away fan.
I presume that RBNY keeps its marketing efforts secret, probably more from embarrassment than strategy. (I cannot imagine any other business seeking to emulate the RBNY model!). However, emailing seems an obvious and simple method.