Tue Jul 01, 2003 3:14 am by Sherlog
Fill your hold with some grossly overpriced commodity. That should bring your net worth below the threshold. If you sell the stuff afterwards then you re-cross the threshold and hopefully the game will notice it this time.
Also, there seems to be a glitch in the game whereby you sometimes level up if you do a trade transaction (buy or sell, doesn't matter) where the value is greater than the level-up requirement delta, which is $10000 for the free time after mission 4. This means that there is more than one way in which the transaction I described in the first paragraph can help you level up.
BTW, have you patched your game?