FYI There is only one vendor I know of, fltplan.com, which would let you file under an obfuscated 'dotcom456' callsign. I believe they are the only provider of this service? (maybe airinc?). Obviously there are still other fields available in the ADS-B that would help identify movements, but this is what i've recommended as its also used over the radios, combating the transcribing algorithms using liveatc feeds.