I´m to embarrassed to show how I do....
come on, i wanna see pictures of you crawling behind each of your cabs!
That is exactly what I do, I turn them on approx. once a month, use simply extension cables with outlets, it does not last longer than a minute, for 25 cabs.
That's what I do too, nothing fancy: extension cables with a switch on it. I put them along the side of the cab so I can reach them easily.
(I try to buy them in black so all you can see in the dark is the red light of the switch)
Personal superstition: I also tend to turn on the step-down converter first, then turn on the cab itself a few seconds later.
I rarely turn all my cabs at the same time so I don't mind spending a little time turning them on.
I also move them often (when I need room to work on them or when I buy/sell new cabs) so I found out the extension cables is a very flexible solution for me.