The dry ice method is one that is supposedly useful for removing dents in car panels. The effectiveness of this is questionable however the theory is that you place a small piece of dry ice directly onto a small dent. The metal in contact with the dry ice contracts which causes it to pull back in place.
Whether this trick works on cars, I cannot say, though I am doubtful. Even if the metal did contract enough to pull up even with the surrounding metal, what happens when the metal warms up and expands? However, if applied to a metal tube the best you could hope for is to pull the metal up far enough to create a flat spot. In order to restore the round shape you would have to pull the metal back up somehow.
Nonetheless, a small piece of dry ice would be pretty inexpensive if you wanted to try it. I doubt that you would damage the paint. You certainly will not damage the tubing with it.