Support referring to order frequencies by their concept (uuid or mapping)

I am writing a javascript client where I need to create an order with frequency = "one time". I am not confident that the UUID of that order frequency is going to be consistent everywhere.

Instead I would like to be able to put "SNOMED CT:307486002" in a constant in my javascript app, and submit this as my frequency.

(This should be easy since RESTWS-468 is already implemented.)