You need to be there because along with his signing his rights away the judge has to ensure he understands it means he essentially is no longer the parent to the child and never will be again and the judge will make sure you understand it means you are completely responsible for the child for the rest of its life .
I really it's not actually easy to have a parent sign away their rights especially just to avoid child support. Child support is considered the right of the child to be supported financially by both thier parents, and I he signs his rights away the government then can't go after him for money if you end up needing money from them .
I don't think you should be letting him get out of his financial obligations either , he should have to support a child he helped create,