Dear Anthony,
you are correct, you have to run another instance of IB Gateway using a different API port using the paper account credentials (these are different then your live credentials) and the second IB Gateway instance must use separate settings folder.
Then you start second instance of PTL Trader and connect it to the API port of the second IB instance.
This works (used this setup for about a week), but I remember there used to be some issues of running two IB Gateway instances on same machine (not sure if IB fixed all of them already)...therefore I recommend to run the paper account setup (IB Gateway + PTL Trader) on another VPS instance for better stability. It seems IB developers have not fully tested the IB Gateway running in multiple instances on a single machine.