Choose The Device That Volume Media Keys Control?

Specifically, this applies to the Logitech G510 keyboard, but concerns any compound HID device with media keys and USB audio.

In Windows 7 (Ultimate x64), it seems the default behavior for handling volume changes from media keys is to apply them to the default audio device. That is, unless the device sending the volume keys happens to also contain a soundcard, in which case Windows applies the volume changes to the device. On the surface this makes sense, but in practice it can be mildly annoying to some people. Consider the case with my keyboard: on most days, I have a plain old keyboard with media keys. My media keys control iTunes in the background and change my default system volume. Works great. But my keyboard has ports for a headset w/mic. When I plug in my headset my plain old keyboard is now keyboard+media keys+playback device+recording device. Now, Windows decides volume media keys originating from the keyboard should be applied to my headset volume. Bummer.

This is what I'm looking to change. I want the volume keys to continue affecting the default playback device (my headset has inline volume control). I'm hoping it's just a registry edit, but I'm willing to pick apart whatever I have to to make the change.

PS: It may be worth noting this only applies to media keys using USB scan codes. If the device happens to use the PS/2 scan codes for Mute, Vol Up, and Vol Down the changes are applied to the default playback device. This provides another alternative way of changing the behavior: if I can remap the action taken for the USB scan code to the action taken for the PS/2, it would also accomplish what I'm after.