Because both signals are not mixed on the hardware level, it surely is possible given you can change the right parts in the system. Which doesn't mean it's easy.
I don't know for OSX 10.5.7, but OSX 10.6+ has a multitouch private API which allows you to intercept click and tap events from the device from a software. Unfortunately, it doesn't seem to expose the physical clicks and it's not well documented.
Here is a program that re-interprets 3-finger taps as a middle click (only source): https://github.com/cl3m/MiddleClick This could be the foundation for what you want to do. Either find a way to get notified of the click or change your requirement to 3-finger taps.
Update: I was a bit fast reading the code, thought differentiating clicks from taps was possible.