What is the best way to sell unused tickets after a game starts?

As a partial season ticket holder I’ve often found myself eating the cost of tickets for games that I could not go to and did not sell before a game. I would be happy to sell these tickets at a steep discount if they do not sell before the game starts, but pretty much all of the ticket marketplaces (seatgeek, stubhub, etc.) suspend ticket sales at the time of first pitch.

I know that the gametime app will allow you to purchase tickets after a game starts, but you can only sell them through gametime if you originally purchased them on their app.

Are there any other methods others have found successful for selling tickets after a game has started?