This is where you have to bite the bullet, so to speak. If you look at those ports, somewhere on the top is listed the bore size. That's pretty much how accurate it has to be, so you can find maybe an appropriate size piece of wire or a tiny drill bit, etc. to clean it out.
But in my opinion, the problem will be back since there is crud inside the booster line. I'd recommend just getting a new brake booster line, shouldn't be too darn expensive.