No, not the switch with blend, I mean the concept of blend with series. With parallel you are taking the output of both pickups and blending between them, effectively blending between two pickups. With series the output of one goes into the base of the other - so the output of the second is the sum of both, making effectively one big pickup, so there is nothing to blend with, and even if you did the output of one will be twice the output of the other so it wouldn't work, it would be the same as blending with a coil tap