Hello and welcome--
First of all, Medicaid is not eager to pay for long-term care at a residential facility either....so regardless of what the insurance rep may tell you, Medicaid is not going to be the "magic solution" to get the child into long-term care.
I think your idea to do a complete medication-wash is a good one. How to get this accomplished....I'm not sure.
Can his doctors have him admitted to the psychiatric hospital for a medication-wash? That should not be technically a "long term" stay...so the insurance should cover that.