ActiveResource and a nested resource routes

I have a nested resource in a Rails app, like this:

  /users/:user_id/actions/:id

I am trying to ActiveResource to access this resource remotely. Now if I name the model "Action" it will search the host for:

  /actions/:id

So I need a dynamic prefix on the url, with an includes a user id. I see various methods in the docs about setting prefixes, but I am not sure exactly which to use and how to pass in the user id.

Anyone got a simple example?