Hi,
Yes you can do that on a non-slim PS2, however the ground point is in the middle of the board as opposed to the edge. On a 'chubby'-type PS2, at the edge of the board is long exposed copper edge - this can be scraped back and the same trick used. Or, use the large copper pad at the top end of the motherboard (by the GH number which the diagrams will probably point to)and run the wires down to the points below (though then your wires are then needlessly long).
The SCEX point is the wire used for PS1 backup authentication. Link that point to the 'SX' point on the top end of the chip. It is optional to fit it, however PS1 copies will not boot without it...
EDIT: Watch out on the diagram too - use the alternate A, B, G and I points (the ones not on the large BGA with fine legs) - don't connect two sets of wires to those points
