Kachi, I had a similar problem but with "power leakage" near the keyboard control section of a proprietary computer photography system. (aka QLT Futura 100) The system was inop and I had spares and could see no way of repairing the board save removing that entire section and reconstructing.
What I did and it worked (albeit with lots of jumpering) Is I isolated the section of the board as best as I could (just the traces associated) cutting traces that might be connected to other critical sections and removing chips that might fry. I then chose an area closest to where I thought the leakage between the two power sections was (that were supposed to be separate) and hooked up opposite poles of a 24v battery to each side and I blew up a small piece of the circuit board (it phyically blew a hole in the area with a big pop) I then proceded to drill out the area and jumper and solder all the butchering I did in the area and reseat all the chips I removed in the area.
How badly do you want to find the leak? If its just a simple trace bridging the planes and NOT a big solder plane a "SAFE" momentary voltage is a common 9v battery, just remember that you need to remove any current paths that are necessary, sometimes there are none between the planes and no connection with chips, other times you may need to unsolder VRMs and such or break a ground trace that may lead through something blowing it out. Its not pretty but this technic does work, although you may end up with a lot of work if you don't verify isolation and blow up things that aren't supposed to blow up.
Good Luck
KachiWachi wrote:
I was going to ask you to do this at one time, but I found out that my Amptron PM 7900 (M520 clone) has a short in the VCore - V I/O circuit...so I cannot power a split-plane CPU.

I even bought a VRM module too.

I'd still be interested in this at some point...if and when I can find the short.
Thanks.