I believe they are talking about canned air, not an compressed air gun. when inverted the propellant in the can is shot out, instead of the air, which will come out as a supercooling liquid (for the second before it evaporates) it works the same as dry ice.
http://www.wisebread.com/remove-car-...ly-and-cheaply
should be the second one on the page...
this won't be a flawless job, of course. if you want your car to look stock (or better) you'd have to have a shop do it...