It's possible, it just depends on what effect you're looking for. Like a Luftwaffe mottle, without an
airbrush it's going to be hard to replicate the feathered look.
I did see a chap do it with pastels. He primed the kit first, and then ran the pastel along the panel lines.
To seal it in, a coat of varnish was sprayed over with a rattle can.
Even with this method, you'd still have to subtly blend in the top coat - not easy with a hairy stick.
Or perhaps oil paints might work - they can be feathered & blended very well.