There are a few ways of achieving it. I went under the main PCB and soldered direct to the track for the second +21V feed near C110 as I didn't want to drill any holes. I also mounted the two tertiary regulators component-side up, unlike Paul, as I found it easier to guide the silver wiring that way. I also star earthed everything except the +5V supply across D301 which Paul identified as critical for a short path.