disable scroll button in XP

I support an ergonomic mouse that internally is similar to a standard 3 button (non scroll wheel) USB mouse. I have been asked by a customer if there is a way to disable the middle button, which is normally used as a scroll button (a button, not a wheel) so that it does not scroll or have any function at all. This is for Windows XP SP2.

I cannot find anything in the control panel mouse applet nor in the registry where this can be done. There is no specific utility software for this mouse and it just uses a standard HID compliant driver.

Would anyone know of anything specific?