Topic: RESTful redirects

I'm using the restful_authentication plugin and here's the situation.  I have routes that are setup as such:

map.resources :users
map.signup '/signup', :controller => 'users', :action => 'new'

And the UsersController#create action:
def create
  @user =[:user])!
  self.current_user = @user
  flash[:notice] = "Thanks for signing up!"
rescue ActiveRecord::RecordInvalid
  render :action => 'new'

However, when a user is signing up, if the model is invalid, the rescue block renders the 'new' action, which in turn transforms the URL into '' (and displaying the error messages in the view).  How can I get the URL to stay '' instead of '/users'?

I tried setting up routes like this:

map.signup '/signup', :controller => 'users', :action => 'new', :conditions => {:method => :get}
map.signup '/signup', :controller => 'users', :action => 'create', :conditions => {:method => :post}

But to no avail.  I can always just redirect to the signup_path after catching the RecordInvalid exception, but that wouldn't show the error messages in the view (using standard error_messages_for stuff).  Any suggestions?