With great care :-)
I have a set of needle files I use for cleaning up putties on difficult seams. I find a triangular needle file reaches down into the notches on that kind of nozzle fairly well. It is still a lot of work, since you have to do each notch individually, and that will teach patience or character, or else help you decide modeling is not such a relaxing hobby :-)
Just kidding, you'll get used to it. Hopefully the model you are building doesn't have too many nozzles!