Like carve out a place between Russia, Belarus and Ukraine in the former Pale of Settlement. Establish a bunch of Yiddish language schools there. Have it become a center of Jewish culture. Sure, there are already Ukrainians, Russians and Belorussians there but there were already people in the far east too.
Ukraine had a fairly large Jewish population before the holocaust. I think out of the 6 million Jews murdered during the shoa, 800,000 were Ukrainian, which is the second largest contingent after the Polish (2 million) IIRC.