Canute The Great was Danish king who conquered England in early 11c. His mother was a Polish princess Swiatoslawa (if i remember correctly) so he was half Slav. Somewhere i read that, when conquering England he used Polish troops sent by his relative from Poland. It might be that some stayed there permanently as garrison troops, or even brought their families. It might also be that he invited some colonists to strenghten ethnic background for his rule.
Also it turned out that there was a substantial (for those days) movement of people between Scandinavia and Rus'. For example, i read that Vladimir the Great while being in exile in Scandinavia met "many of his countrymen" if i am quoting correctly (This is unclear weather it meant Varangians from Rus' or Slavs from Novgorod or that it made no distinction between them). So it is feasable to assume that Slavs, or at least some of them individually, could have appeared throughout northern Europe via that route.