I didn't attempt this, but I'm pretty sure that you'd need to get the method code for:
Code:
[MethodImpl(MethodImplOptions.InternalCall, MethodCodeType=MethodCodeType.Runtime), DispId(0x60030020)]
void Register([In, Out, MarshalAs(UnmanagedType.BStr)] ref string LiberationKey);
The code seems to be generated at runtime, so try dumping it.