Yamaha DTXpress/DTXplorer/DTXtreme

This might seem kinda crazy, but I purchased the game Rock Band which 
comes with a crappy electronic kit. One of the worst things about this 
kit is the bass pedal. Well, I own a DTXpress III and the back of the 
Rock Band kit has a 1/8" mono input. I tried hooking up the KP65 kick 
pad from my DTXpress kit up to it using stereo cables, mono cables, and 
mono to stereo, mono to mono adapters, etc and nothing seems to work. I 
don't completely understand how the kick pad works, but I'm guessing 
the problem is that it isn't a simple on/off type switch. So I would 
think I'd need to build something similar to Keith Raper's Piezo/Piezo 
to Piezo/Switch Adaptor but possibly in reverse? It would take the 
output from the KP65 and then create a single mono on/off signal that I 
could hook up to the Rock Band kit. I hope I explained things well 
enough. Is there anyone that can help?