I've never heard of anyone thinning bondo & spraying it but that isn't saying it can't be done although I think the thinner would mess with the chemical reaction. Last week I saw a product at the body shop doing the work on my 38 that is a sprayable body filler that swells as it sets. It won't fill large dents but they say it works well on minor imperfections. I don't have a name for it or where to buy it.

Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.