[Avodah] Mitsvat Sukkah is almost unique

[Dov Bloom]

The mesorah of RSZA and his talmidim especially R Nebenzhal in the name of the GRA about Graf Potocki and Ruah Ra'ah in the morning is also mentioned by R Moshe Harari in Mikraei Kodesh Hil. YK p 157 (Perek Zayin in footnote 17). 

R Harari adds that true convert R. Avraham ben Avraham (the Graf Potocki) was tortured by the monks, who threatened to burn him unless he re-converted to Christianity, which he refused. The GRA offered to save him using Sheimot HaKedoshim, but the ger tzedek refused, preffering a "kiddush shem shamayim barabim" . 

Harari quotes R Nebenzhal saying that this mesora of the GRA is not found in any written source but alluded to in the book HaGaon HaChasid MiVilna p 18.

Does anyone know of any other sourcces about this mesorah from the GRA not coming from RSZA and his talmidim?