As you probably know, cocoa butter is usually used. If you were spraying to get a high gloss finish, then I don't think butter would yield good results- once dry, the result would be very matt and dull. To achieve a gloss finish you would have to add the butter to the chocolate below 30Celcius and then it would be impossible to spray (you would have to reheat it-but this can lead to a dull look also, but less so)
On the other hand, if you were to spray a frozen cake to achieve that velvet effect, then it could possibly work, it'd probably have a different mouth feel - but might be worth a try if you can't get your hands on cocoa butter.
yeah , i was trying to bulk out cocoa butter , i want to coat a semi freddo/ iced parfait but dipping creates too thick a coating , and was thinking spraying would get a thinner cover. mmmm? a quick blast with the torch en voyage may combat the Matt effect.