I think I've figured it out.
The tweak should be loaded in mediaserverd daemon. This can be done by editing the .plist of the tweak. There should be an Executable
filter in the plist:
Filter = {
Executables = ("mediaserverd");
};
For more information about CydiaSubstrate (MobileSubstrate) check:
iPhoneDevWiki - MobileSubstrate
And I think this tweak is only for iPhone 4S and above.