I have heard of guys cutting 1/64 grey and black monokote strips for panel lines, athough in my experience they tend to fall off, and would probably need to be overlaid with clear monokote if you didn't wanna have them all falling off in a few weeks.

In which case that's a little out of my depth.

Thinking about it, the biggest issue is going to be adhesion to the film, and then protecting it enough that you don't rub it off when cleaning it (even electrics need a clean once in a while!)

I have in the past toyed with the idea of using a beugler pin striping tool for trim lines and panel lines, which would mean you could possibly fill it with something that will stick to the monokote, but you may well be the first person to do so.

Excellent, I was about to have a poke at the wobbly line just ahead of your flap when i realised it's actually a scratch on my screen!! 

Paint as Dave points out, can work pretty well, but you have to have paint that will stick to milar. You can ink it more conventionally (with a pen and ink designed for milar) then shoot catalyzed polyurethane over the Monocote like a clear top coat. That will stick.