Problem with dual extruder printing, oozing

Hi all,

I have a problem with the dual extruder printing. I am using two colors filament at the moment. White and Black. The printer has both extruders heated up at one moment during the printjob. Causing the second nozzle to “push” leaking filament into the print. So the end result is a lot of black spots and stringing material into the white surface.

Is there a way to make sure this does not happen. Ofcourse the printer is adding an ooze shield and tower but this is not helping either. I was thinking if there is a way to heat one extruder at the time and wait for the other one to cool down completly so that their will not be any leaking material. But I have no idea how to add this code?

Can someone help me out? I am using repetier and the cura engine.