I dont' believe you can install a second instance of Reporting Services (it is after all only one windows service).
However, try creating two folders, one to represent development, one for training and rollout. You can then create a Data Source in each folder (one for dev, one for training), name them the same thing. Make your reports use the shated Data Source name.
Then develop your reports in the development folder, with the development data source. If your data source name is the same for both, you just need to upload the report to training when you are ready.