Well, if you notice any cranial leakage Stop Blowing!!
Seriously though, you certainly do not want to trap any significant pressure and be left with a residual sinus headache. Often these are caused by day to day changes in atmospheric pressure, so quite a small diff can be tedious if it is locked in.
Let pain be your guide, as the physios say. But whatever you do it would be doubtful that you would achieve the pressure diff of totally blocked sinuses at a typical cabin altitude round 35,000 feet. On the above mentioned flight, I had no lasting injury, and there was no bleeding despite spending 2 hours in the cruise in severe pain. we landed in Tunis and I had no pain at all for a blissful 30 mins. On the way home we were worried about fuel and pushed up a bit higher. It totally disabled me.
I was also concerned that it would suddenly equalize and leave me with a huge pressure diff while on the ground;at least as it was, I knew the pain would stop on landing.
So, I'm suggesting that you listen for the little squelching noises and use them as an indicator of when to stop. Proceed slowly, you only need a tiny fraction of the mixture to start to work its way in. If all's well, be a bit more adventurous next time.