I saw a post here, can't remember who from, but he posted an image for 5V supply to the 360 nand, that you could use instead of plugging the PSU in.
The image was similar to this.
When I checked those points with a multimeter, they actually read out 3.3V which is what voltage the nand needs.
Putting 5V across there would be dangerous to the nand I would assume.
I decided to look for a point where I could apply 5V and use the boards components to reduce it to 3.3V.
Looking around with a multimeter I found this point which read out 5V and is conveniently on the same header as used for the nand programmers.
I'm wondering if that would work at all? Because then I could just use the 5V straight from a USB nand programmer to power the chip instead of plugging the XBOX in.