You can't do it.
Or, more to the point, you can't do it practically.
The impedance mismatch makes it impossible to wire a passive pickup and an active pickup together directly, though it IS possible to do so if you use some kind of buffer amp on the passive pickup, but that will have some effect on the sound of the pickup. Not a lot, and probably not a bad one, but an effect none the less.
The good news, if you go that route, is you can use the same battery for the Blackout and the buffer. If you really want to do it (I don't recommend it), I'd suggest a Bartolini preamp. I'm not sure what the model is for the just magnetic version (as opposed to the two channel magnetic/piezo version), but I'm pretty sure it is not on their short list of regularly made products so it will take a while to get.
Light
"Cowards can never be moral."
M.K. Gandhi