Hmmm, well damn... Russia had a real chance to be almost right next to Pomerania in the reign OF Ivan the terrible.
He was offered the throne of the Polish Lithuanian Commonwealth (as one to be elected) TWICE during his reign. Change his attitude a bit, and instead of having the Frenchman sit on the throne of Poland-Lithuania for half a year, you get Ivan the Terrible on the throne.
Admitedly, this would actually be more of a Russian-Polish-Lithuanian Commonwealth than the Russian Empire, but if you have Ivan the Terrible on the throne for a while, and then have his son Ivan (the one who he killed) take the throne of the triple Commonwealth (he was said to take after his father alot) then you could probably have them force it into being a heridetary triple Kingdom.
From there on in, the Rurik's might be alble to have ALL kinds of fun in the 30's years war.
So if you'd move the POD just back a smidgen to the reign of Ivan IV, you could have the Tsars of Russia (also kings of Poland and Dukes of Lithuania) beat the Swedes to it and make the grab for Pomerania themselves at the end of the Thirty years war. This near domination of the Southern Baltic coast could have the Ruriks clamouring to subdue Sweden in order to transform the Baltic into a "Russian" lake.