Rails route: adding helpers methods

Question

I am coding an API in rails, and the following scheme appears multiple times in my routes.rb: (The goal is to link existing devices resource to users one.)

  resources 'devices', controller: 'users_devices',     only: [ 'index', 'destroy' ] do
    post on: :member,                                   action: 'create'
  end

I would like to have a "route extension" that would allow me to do this:

relation 'devices', controller: 'users_devices'

Much more readable and since I have 5 times this same 'boiler plate' code, it would simplify the routes.rb

But... How can i code this "relation" method ?