How may I involuntarily terminate the parental rights from a parent who has not been involved or in the same state as the child for 6 months or more?

if he wont agree (voluntarily) i don't think 6 months of no contact will do. You need a lawyer. Wait till one year passes and file a petition for termination based on abandonement. It will be alot of work and expensive. And, if he fights it, or files for visitation, you may lose.