<brag mode on>
So I had a broken motherboard from a customer who tried to install a cheapmod on a 1.3 motherboard and used the MCPX lframe. They broke the trace and a couple surrounding traces, and the Xbox obviously didn't boot.
I had another nonworking motherboard staring me in the face with a good MCPX, so I figured, "why not?"
I don't have BGA equipment, but I removed both the good and bad MCPX with a SMD hot air nozzle, cleaned up and prepped the BGA points on the board and chip, spent a few minutes making sure everything was lined up, and heated the MCPX back up with the hot air nozzle.
It's hard to judge when the solder has reflowed when you can't see it under the chip. But I took a guess, after a couple dozen seconds of hot air, let it cool and tried booting the mobo with transplanted MCPX.
OMFG it booted!
I WISH I'd taken pictures throughout the process, but didn't think it would work. Maybe for my next transplant!