They'd have to put some sort of limit on the number of seats allowed over the demand for each airline or like a percentage. So like if the percent is 10% then a route with a demand of 50 in economy would only allow 55 seats per airline and if the demand was 2000 in economy, the route would only allow 2200 seats per airline. My dad says it would be easy to implement because it's just a limit, and he works with code, so I think he knows what he's doing.
The only problem I see is for regional jets with less than 100 seats. So if you want to send a CRJ200 with 6 business seats and 30 economy seats, it wouldn't work on a rout with a demand of 27 or less because of the 10% over limit. Perhaps on these routes they could just set a plain limit of 30 seats for demands 20-30, 40 seats for demands of 30-40, 50 seats for demands of 40-49, 60 seats for demands of 50-60, 75 seats for demands of 60-75, and 100 seats for demands of 75-100.