sinatra/mount

mount.rb

module Sinatra
  module Mount

    def mount(app, route="/#{app.name.downcase}")
      %w{get post put delete patch options}.each do |method|
        self.send method.to_sym, "#{route}*" do
          app.call(
            env.merge!(
              'SCRIPT_NAME' => route.split('/').last,
              'PATH_INFO'   =>  params.delete('splat').join('/')
            )
          )
        end
      end
    end

  end
  register Mount
end

Usage:

require 'sinatra/mount'

class Foo < Sinatra::Base
  register Sinatra::Mount

  mount Bar, ':foo/bars'
end

Note: the splat pulls in whatever follows, trailing slash or no trailing slash

Looks it working well :)