I held it down with the tips of the fingers of one hand at the base of my shaft when I was a child. Otherwise it would shoot forward instead of down. I recall being pleased one day to discover my penis was long enough that the stream now went down instead of out. That was a long time ago.
Most of the time, I adjust myself when I sit down, and I'm fine. Like others, I've had a few times where I didn't adjust and the head of my penis shot the urine out between the bowl and the seat, getting the back of my pants wet. When I find myself having to sit on a toilet that is in serious need of cleaning, I may push my penis down so that the head doesn't come into contact with the bowl, but that isn't often (thank god). I've never really thought about it until you asked, but I tend to use 2 or 3 fingers, usually the index, middle, and maybe ring fingers on my right hand (I'm right handed) and I tend to place them along the length of my penis while I push. Most of the time, due to the middle finger being longer, only 2 ever touch it. In some cases, I may lean to my left to help adjust the angle, but not often.
I too have had prostate removal and when sitting to pee, I use 1st three fingers and the thumb to hold it in the correct position so as to not pee all over the place including between the seat and bowl. Standing pee is accomplished by holding it with all fingers and the thumb with a slight stretch to get long enough to clear all clothing and improve the aim.
When done, a couple of shakes to remove drops ... and it just feels good .....