I also agree that something needs to be done about this, it makes no sense for 5th place to be more desirable than 3rd or 4th. Paying half the salaries might do it, but it's a bit hard to think about it logically. Basically you're saying your players are paid half their salary.
My suggestion would be to boost the TV contract for teams participating in the playoffs. You don't have to increase it too much, just enough for the teams eliminated in the first round to break even. Or if this can end up giving too much cash to the teams with home-court advantage that get to the finals, than just a one-time "making the playoffs prize money" that would be roughly 2/3 of the average gate receipts of the teams participating in the playoffs, so that you end up getting a "normal" gate receipt for that weekend.