Rather than seeking waiver, you might have better luck seeking modification of the amount owed due to the decrease in income while in prison.
Stew Crawford, Jr., Esq.
Crawford Law Firm
A Full Service Law Firm Serving Individuals and Families in Pennsylvania & New Jersey
223 North Monroe St.
Media, PA 19063
Support arrears will accrue while a parent is incarcerated. Once released, the arrears are due and owing. However, the amount of the payments may be modifiable based upon your current earnings/earning potential.
My response is based solely on the limited information contained in the question. It is not meant to substitute your attorney's advice.