Wis. Stat. § 51.63

Any person may pay, in whole or in part, for the maintenance and clothing of any mentally ill, developmentally disabled, alcoholic or drug dependent person at any institution for the treatment of persons so afflicted, and his or her account shall be credited with the sums paid. The person may also be likewise provided with such special care in addition to those services usually provided by the institution as is agreed upon with the director, upon payment of the charges therefor.