If the sleep button is driven by third party software and not by the operating system itself you should be able to activate the controlling program and change the behaviour of individual keys including the sleep button.

As already mentioned not running the software that drives the additional keys at startup would also be a good solution if you don't use any of the other additional keys.

If the sleep button is driven by the operating system you can disable the service that allows such additional keys to function. The link below provides information about the service.

Human Interface Device Access (if SP2 is not installed it is called HID Input Service)