This can be done by:
1. Run the restore job on DR server
2. Take a tail log backup on Production server - This will leave the database in a restoring state
3. Restore the tail log backup to the DR server.
--Switch back
1. Take a tail log backup on "new" Production server - This will leave the database in a restoring state
2. Restore the tail log backup to the "new" DR server.
This will leave your original Production database as the Primary database.