Interest on Child Support Arrears

Hello!
I love the new message boards! I have a most unusual question. Here is the Reader's Digest Condensed Version:
Ex and I divorced in 96. He didn't pay child support for 96 weeks. He racked up quite a bit of arrears. He has finally paid of the arrears, but still owes quite a bit in interest. DHR has informed me that as the interest is paid to me that I have to claim it on my taxes as it is INCOME. The ex is having problems getting home owners insurance, credit cards, etc because he has this debt on his credit report. He and I have come to an agreement. He will continue to pay the same amount he is paying now (current support + arrears) if I agree to have the interest dropped. That way I am still getting the money, but it is counted as support - not interest and his credit is cleaned up a bit.

DHR has said that if I close my case with them that the IWO will stay in effect with his employer but the payments will go through the AOC (GREAT - they have direct deposit!!) and DHR will not pursue the interest through tax offset any longer... but what I am wondering is - how do I get it erased or forgiven or written off or whatever you call it? Is it as simple as a joint petition to modify?

Another side note - the ex and I used to HATE each other. If you look back on the OLD message boards - back when Lee was still Uncle Lee - then you can read some of my very hostile and angry posts. I have since gotten over my anger and he has since grown up. He sees our daughter regularly, takes off work sometimes when school is out, and is being a good dad. The interest is causing a friction that I'd just as soon erase so that our daughter can continue to enjoy her parents getting along well. Any help is GREATLY appreciated.