Do airlines staff extra crew members when disabled persons are check in? The question "How are disabled passengers evacuated during emergency?" made me wander if minimum crew number required by regulation are enough in case of passengers requiring extra care in case of evacuation.

My question is restricted to cases where airliners know in advance that a passenger with reduced mobility, unable to run or jump (let's say the passenger requires either a wheel chair or crutch to walk) is scheduled on a specific leg. Do airlines staff extra cabin crew member(s) to improve handling of everyone in case of emergency evacuation?
In almost two decades of flying for airlines, I've never seen it done, and never heard of any program to facilitate such staffing.