I added the v4 pop-fix to my v3 board by placing components directly onto the v3 board.
Start by drilling a small hole (0.7mm in my case) to the right of R70 so as to be able to fix the 2N7000 transistor. Pin 2 of the 2N7000 is soldered on the underside of the board (ground).
Scrape a little varnish from the tracks and tin ready to fix the 2N7000.
I added some Kapton tape to stop any shorting of components.
Add the remainder of the components and run a bit of enameled wire to the trace near the raduino headers to pickup the T/R line.
Ignore the cutouts on the front of the board, I had to hack away a little to clear the 3.5mm sockets on my case (I had to add a small length of enameled wire on the underside as I had hacked through a board trace).
So far, so good with no problems to report.