What I didn't factor in was the element of sync, which happens to be quite crucial for legible video. As it stands, it would appear as if the WJ 545P cannot lock to a composite video signal at the PL-259 input (my abilities as an operator may be at fault here). At any rate, having the option to power the camera at the SEG is enticing, whether or not this will sort out my sync issues remains to be seen.
I believe I've already taken pictures of drilling metal, so let's just skip to the result. +12 volts at roughly 500 mA is fed at pin 10 (pictured with the blue wire sans heat shrink), referenced at pin 9 (behind the blue wire). Naturally the surrounding pins are to be left alone.
Not a whole lot of room to work here.
Here's the result. Some liquid electrical tape that was used to insulate the ends of the disconnected wires, since I have misplaced my heat shrink. The idea was that the end result would be cleaner than electrical tape which can unfurl over time. I wouldn't call this cleaner, so I'll just comfort myself on the permanence aspect.
A bit of heat & melt due to space constraints, could have been worse.
So there you have it, DC power input for camera channel 1. Since the SEG supports only two channels simultaneously I didn't see the point in modifying more than one input, as I have multiple SEGs that will cascade into one another (forming a loop if I choose) and the power supplies I have earmarked won't support more than a single camera. I'll just allocate channel 1 as a powered input for each.