Figure out how much money a private company would pay in taxes on all the land Lehigh’s using, and then send them a fake bill for it. Make sure the press knows how much it is. Then figure out how much less the average homeowner’s tax bill could be if Lehigh paid the equivalent of their land tax bill to the city, and make sure the voters know what that number is.
This would be more embarrassing for Lehigh than an arbitrary amount like $1 million. You need to show people the actual amount of money the city’s losing every year with all Lehigh’s land off the tax rolls. Count the amount lost to non-profits on the spending side of the city budget every year so it’s in people’s faces. You need to start acting like you expect them to pay the land tax, not like you’re begging for it.