Mirror Rails 3.2 requests to a Rails 4.2 staging server?

I am currently in the process of upgrading a Rails 3.2 project to Rails 4.2.

While all my tests pass I want to run some more realistic tests before going live.

Is it possible to 'duplicate' all requests coming in to the current Rails 3.2 production server and execute them on the Rails 4.2 staging server?

Both run on the same machine. Both use a different database that I can re-clone from production at any time.

Any exceptions that occur on the new Rails 4.2 staging environment should trigger an email alert which allows me to compare the 2 and fix those particular errors, should any arise.

EDIT: The mirroring does not need to happen live. Perhaps there is a way to log all requests and parameters, etc. over a period of time and then 'replay' this log on the staging server, starting with a specific snapshot copy of the database.