I've done these a couple of years ago, exclusively using brushes:


Basically, I used the following steps:
First, apply the darker base colour, in this case a dark military green.
Next, apply the light splotches by painting them in as normal.
Then, using a stiff, small-diameter brush, stipple on extra amounts of the light tone to obscure and soften the hard edges. This would ultimately need to cover the dark tone and blend over the edge, but fade towards the darker area.
Following that, both tonal areas are highlighted towards the area centres using drybrushing and stippling.
Applying a thin wash over the whole assembly, or possibly only pin-washing the crevices and panel outlines, can help in unifying the various tones.
Basically, it can be done in reasonable time and steps (the Hind took me the better part of an afternoon to do the camo on). Obviously an airbrush will be quicker, but may take more practice, especially if you already have experience with drybrushing and stippling.