The person you work with should see a doctor first to figure out what causes their RLS (fibromyalgia has RLS as a side effect).
Once any underlying condition is ruled out, have them move. RLS runs in my family and we do lots of cardio to help offset this condition.
I make exercise recommendations for all sorts of conditions, so I personally do not worry about scope of practice but may require a physician to sign off a form on which s/he could indicate restrictions and often ask the client to bring the exercise prescriptions from physical therapy as appropriate. Here is a link to more information http://www.rls.org/Document.Doc?id=2157.
RLS is one of those strange things where exercise in general helps but when and what is often a matter of trial and error. I do not know of any exercise for RLS alone that is contraindicate but the client may have other circumstances such as poor posture which may set limitations.