This has been asked, discussed and answered so many times, and we were so *sure* people would ask for it, that we put a clear not on the GSX manual about it.
There have been countless of discussions on this forum, and complete explanations about the issues involved. The short answer is, is something we have already looked into, and GSX will have it in the future, but we can't promise any date for it.
For the time being, just enjoy GSX for what it ADDS to FSX (and it surely adds at lot), rather than worrying about what might be added to it.