Using our newly-discovered technique of tin-plating the entire PCB then soldering the 0.05" pitch IDE cables using solder paste, we managed to create some ready-to-try boards quite quickly this evening.
The cables were soldered quickly and easily and the joints were strong and consistent; no messy de-bridging with solder braid was needed (which often causes the pcb tracks to heat up too much and start to burn or lift)
A final, populated board, with a PIC18F2455 in place and extra components to make a USB HID device. This was an early board and we'd already attached what will become the USB socket using the "old-fashioned method" of drilling holes, splitting the cable ends and pushing them through to solder on the underside of the board.
Maybe with this new technique, we'll be able to either use SMT chips OR trim or bend the pins on the larger chips to enable us to solder them directly onto the (tinned) traces of the board without having to drill the through holes first. If that's possible, it will mean making PCBs would take a fraction of the time it does at present: it's all the drilling that takes forever and the less drilling we can get away with, the better!
Of course, for this board, we still need two rows of 6 holes for the strings to go through, but for future boards, we'd need only a few holes for things like the crystal and 470uF capacitor (although there are SMT versions of these with relatively large pads available too.....)