I make a lot of use of reflectors to reduce shadows (everything from proper reflectors to bits of paper, card, tin foil, pages of a book... whatever comes to hand first, you name it.) Does that count?
Not exactly a hack, but using one layer of hosiery stretched over the lens and fixed with an elastic band can provide a nice "soft light" filter effect. Different hose can give you interesting different tone.
I love shooting still life resting on top of the dull side of aluminum foil. It gives subtle reflection, gives great back drop tones, and looks a bit unique
I don't know if this counts as a hack or not but I made a snot for my flash to get the selective lighting on my face. I just wrapped a piece of navy card stock around my flash and held it in place with a rubber band. (If you don't want the color cast then use black)
My hack is pretty common. I opened up my D70, removed the hotmirror filter from the top of the sensor, and replaced it with a Infrared bypass filter. (protip - If you decide to do this, keep your fingers away from the flash capacitor as there's enough juice to hurt like hell)
I am generally not very good at sets up .. so was dead pleased my mushroom shot worked
Love your cotton wool cloud
Exposure: 0.0025 sec (1/400)
Aperture: f/8.0
ISO Speed: 100
Taking along a syringe of glycerin
and the set up:
My tip is - I use the inside of a biscuit tin to reflect light back onto the shady side of macro or still life shots.
The results are quite fun.
Strategically placed glass pebbles and F/1.8