You can use the Lionel unit, and if you want your dummy unit to appear to require maintenance, use the MTH PS/1 smoke unit. Both will run directly off track power. Switching them is as simple as putting a series switch in the power path.
If you want to get fancy, you can run a small tether to the dummy unit and use a relay to control the smoke unit from the primary unit's smoke power. That way when you shut down the smoke from the remote, both units will stop smoking.
ERR also sells a special module that is intended for dummy units that controls smoke, lights, and electrocouplers, it's listed for $35 on their site.