I suggest you start using jkey.dll as hotkeymodule. Then you can use an app called scankey.exe (which can be found in the utils-section of shellfront.org) and make it "read" the keycode off of the volume-buttons.. then assign names to these keycodes and type them into a file that's shipped with jkey.dll called vk104.txt. Having done that, you assign volume-bangs to your "new" keys and then you're good to go!

Remember to use jkey 0.37, because it lets you use keys without modifiers (ie. Instead of *hotkey WIN NEWVOLUMEKEY !Volume_Up[whatever] you can use *hotkey .none NEWVOLUMEKEY !Volume_Up[whatever]).

hope the short explanation helps.