Point DNS to subdirectory on heroku rails app?

Point DNS to subdirectory on heroku rails app?

We have a rails app that generates subdirectories for a user
example.herokuapp.com/user1directory &
example.herokuapp.com/user2directory
Is there a way to point DNS for a url to that specific directory of the
rails app, without any silly hacks?
Ideally what we need is user1website ->
example.herokuapp.com/user1directory but masks it while showing any
further subdirectories / pages.
Any help will be greatly appreciated.
Thank you.