Although your idea is ingenious, unfortunately it creates more new problems than it solves.

1. The Mishnah in the beginning of Sanhedrin states that Kidush ha'Chodesh needs a Beis Din.

2. The Gemara (Rosh Hashanah 24a) brings a Pasuk to prove that the Rosh Beis Din must say "Mekudash."

3. From the Mishnah on 25a which relates the story of Raban Gamliel and Rebbi Yehoshua it is also clear that there must be a central [body determining] Rosh Chodesh.

These Halachos hold true (in some form) even when we are Mekadesh Al Pi Cheshbon. That is why the Rambam writes that is accepted that even when Rosh Chodesh is declared through calculation it is still only done by the Beis Din in Eretz Yisrael (Hilchos Kidush ha'Chodesh 5:1). If we accept your theory we will have yet another problem with the Shitah of RaSaG.

Dov Zupnik