WIA event callback ... unregistering other callbacks that aren't my own?

I've registered my program to the WIA_EVENT_SCAN_IMAGE event. Ideally, when I press the physical scan button on my scanner, my program will begin scanning without need for prompt.

However, because other programs like Epson Scan might be installed, what ends up happening is that Epson Scan may start before my program can start scanning, and seems to claim use of the device before my program can.

Ideally, I'd like to unregister all other callbacks on load, and reregister them on clo开发者_运维知识库sing.