Nope. Boiling water wouldn't be hot enough, nor site-specific. You'd warp the whole piece you were putting in it, more than likely?
Doesn't matter how "cheap" your irion is--you're only going to use it to transfer heat to a specific area. All you want to do is hold it under whatever plastic part you're trying to dent so that the heat rises into the plastic. Do not use a candle!!!!
This is really an easy thing to do. Just don't be in a hurry, and don't overdue it--keep poking gently at the plastic to see if it's becoming pliable.