Sorry, everyone, for the delay. I've been waiting for my back and shoulder to settle down before fiddling about with the experiments I said I'd be doing.
Below you'll see photo's of three methods from which I could get a reasonable(ish) result. Another three I tried I just couldn't get to work at all. They were:
1. Using a thin strip of decal to wrap the twin run of mono', by wrapping the mono' like it was being bandaged. It near drove me crazy. I had to use forceps to anchor one end of the decal film to the mono', to be able to start. If the decal film didn't tear immediately then it would tear not too long thereafter. Nor would it wrap evenly. In the end I gave up on that idea. No photo's, as I was too cranky to bother.

2. Similar to the above, but laying the decal along the mono' and attempting to fold the film over. I used Experts-Choice white decal film (and it's lovely stuff- for doing decals). Getting an even fold is near impossible, unless you use decal solvent (I was using Micro Sol) to shrink the decals. However, that just causes the decal to split as the mono' cuts it like a knife. Once again, I gave up on this method once my systolic blood pressure reached four figures.
3. Drilling 0.15mm holes in the end of 0.25mm thick styrene strip and gluing the mono in the holes with thin Cyanoacrylate. Don't bother. It's very fiddly and frustrating and it can get the blood pressure higher than method 2, above, in half the time. However, if by some fluke (or by having a well-equipped work bench) you do get all four holes drilled in the strip, the mono' glued in
and leave it all to dry over night (it's really important to let the CA dry properly), this gives a really strong bond and the mono' won't strip out at normal rigging tensions. Then you face another three or more slats to do.......
So what did work?
Making a new, simpler, jig helped a bit. All it was was four sewing pins, heads cut off, hammered into a compressed bamboo cutting board (DON'T TELL MICHELLE, for gawd's sake!) so they gave 1mm clearance between two runs of 0.125mm mono'.
4. Then I tried white glue (doesn't work- the glue kept beading up rather than filling the gap) and Kristal Klear (KK). KK didn't work too badly. It also tries to bead up, but you can smooth it out a little as it dries:

You've probably guessed, though, that anything that uneven isn't likely to dry smoothly. You're right:


On one attempt I got a better finish. Now that run was only half as long and the humidity was right up. Whether those factors had an effect, though, I have no idea.
5. Next I tried a thin strip of cardboard, cut from a business card. This worked fairly well, though I had to nick the corners, so that the card would sit between the mono'. Also be aware that you'll be holding your breath after the first attempt, when your breath causes the card to drop out of the wires. The trick here is to remember to stop and breathe again, in between subsequent attempts.

This worked fairly well. Once I'd got it sitting in place I coated the line and card with diluted white glue. The diluted glue, however, gets absorbed by the cardboard and makes it warp, as you can see above.
6. Lastly, I tried 1mm wide X 0.25mm thick styrene strips. Rather than laying it on top of the mono', as I did with my N.28, I nicked the corners lightly and laid the slat between the mono'. The nicks again helped prevent the slat from popping out of place with every breath. I had run Tamiya Extra Thin polystyrene glue down the lines first, before slipping the slat in, and they helped hold it. Once in place, I very gently brushed some more glue along the outside of the mono', and left it to dry.


The one weak point with methods 5 & 6 is that the mono' easily strips off the card/slat, if it's pulled away from the slat at all.
* Over the last few weeks I've tried a couple of other things, such as using 1mm tape to wrap the mono', etc. They didn't work for me, but they could do for you.
Anyway, I hope someone can use some of these techniques and make them work. You can then tell us all your secrets!

Cheers.
Dal.
* As I was typing this I had the idea of running some KK along the edges of the mono, after the Tamiya glue dries. That may give it some lateral strength. I'll try that tomorrow- the last experiment is still sitting on the board.