I'll try. Do this...

I pull the plunger back normally with my index finger and thumb. Once I have it pulled back I hold it with just my thumb at about the 10 or 11 o'clock position on the knob. I place my middle finger against the cabinet at about the 4 or 5 o'clock position relative to the knob. My hand is than in a similar shape as if I'm using my hand as a pretend gun. Once the plunger is in the position I want I slide my thumb nail off the knob smoothly.

With my middle finger on the cabinet it give me a stable hold to keep the plunger where I want it. Since I only use my thumb to hold and release I don't have to worry about my other fingers catching on the knob. I always do this by feel and never use the guide markers. I am fairly accurate on skill shots, even on games I've never played after a few plunges.