893.15  Rehabilitation.--Any person who violates s. 893.13(6)(a) or (b) relating to possession may, in the discretion of the trial judge, be required to participate in a substance abuse services program approved or regulated by the Department of Children and Family Services pursuant to the provisions of chapter 397, provided the director of such program approves the placement of the defendant in such program. Such required participation shall be imposed in addition to any penalty or probation otherwise prescribed by law. However, the total time of such penalty, probation, and program participation shall not exceed the maximum length of sentence possible for the offense.