Criminal Law Questions? Ask a Criminal Lawyer.
It is true that you can negotiate with the government representative/attorney to settle the restitution. Usually, the government and victim aren't willing to agree to this unless you have a reasonable lump sum to pay at one time.
My suggestion is that you contact a local attorney and ask him/her to contact the prosecuting attorney's office and find out if the victim is interested in this. If so, you can begin negotiations.