title: Add variable prefix to angular routing
body: <p>I am trying to update an old BackBone.js app to Angular (4/5).
  One of the requirements is to keep using the old routes in this new app, which triggers some challenges.</p>
  
  <p>The old routes are build as follows:</p>
  
  <pre><code>site.com/r/{username}/{route}
  </code></pre>
  
  <p>e.g.</p>
  
  <pre><code>site.com/r/johndoe/homepage
  site.com/r/janedoe/blog
  </code></pre>
  
  <p>I'm now using Angular routing without hash, but every route i build in Angular now consists of a long string:</p>
  
  <pre><code>{ path: '/r/:username/homepage' }
  </code></pre>
  
  <p>I'm hoping there is a cleaner way to uses routes in here.
  The :username variable is only needed when bootstrapping the app, so it would be a lot nicer to strip the first bit off of the Url and start NG route paths after this.</p>
  
  <p>I know base href will compile the app to a potential subdirectory, but this will not work with the variable username.</p>
  
  <p>Is there a way to make this work in Angular?</p>