Can you say Shnayim Mikra for Parshas Breishis prior to Simchas Torah?
The Mishnah Acharonah says that one may start immediately after the Chosson Braishis has read his portion.
That seems to be one source on which allced's Rov might have relied.
I now found in Wikipedia:
On the day of Hoshana Rabbah (any part of the daytime), Shnayim mikra ve-echad targum should be read for the V'Zot HaBerachah portion.
which is a leniency. I did not find the original source.
Asked an OR tonight, 12 Sep 13. He says you can start right after the end of the reading for the Chosson Torah i.e. while the Reader is saying the "Reshus" for the Chosson Braishis.