The front coupler output only sticks around for 1/4 of a second when triggered, so it would be a very short whistle. 
I faced this problem with my little clown handcar sound, and I built this little module to solve the problem. This module will trigger sounds based on electrocoupler inputs. I didn't use either coupler, so I had two potential remote triggers. In addition, it has three other inputs that can trigger sounds from reed switches or any other contact closure. I use the BY8001-16P MP3 module to generate the sounds, my motherboard supplies the power supply and interface logic for the MP3 player module.
