My answer would be "no", you cannot use child support as supplemental income.
The underling purpose of child support payments is to ensure children receive the same proportion of parental income, and thereby enjoy the standard of living they would have experienced had their parents remained together. It's intended to benefit the child, NOT the sponsored immigrant.
Just my thoughts. Whether you really can or not, I don't know. Hopefully, your normal income is sufficient. Otherwise, I suggest getting a joint sponsor.