Ahh good point. Well the wire will likely have to go on one of the bolts which goes into the motherboard... or some location on the shielding.. I guess in terms of the STE, it has a metal sheet anyway, so probably wouldn't be a problem for those machines.
STF machines, I think most leave off the PSU cover now, so the wire going to the main metal shielding would be simple enough. Basically people would have to extend the wire.. but in terms of original PSU, I don't think many would go for a new plastic over a original PSU anyway. So I would really say, don't worry about it, and just leave off the plastic part where the wire normally bolts into.
In terms of my new PSU builds, there will be new sockets and switches anyway, so extending the wire isn't a problem.. Will just have to figure that out when its physically installed, and just find the best place to bolt the wire to the metal shielding somewhere.