Nope, completely legal, a little goofy looking, but what ever works. It is only violating the rules if you make a stroke at the ball standing on the line. Long time ago, Sam Snead use to putt mallet style, standing behind the ball, and was really good, then they changed the rules. He still putted the same way, just stood to the side off the line, but still facing the hole.

The rule about touching the green does not apply to setting up to make a stroke. It means you can not use the putter or any other object, including your hands, foot, etc...to test the green, to find out speed or grain. You just have to do that by sight alone.

Oh by the way, no one else may stand on the line of a putt, front or back while making a stroke either. Now once the ball is rolling and the stroke as been made, you can run over behind the ball on the line, that is ok, just not during the stroke. Otherwise their caddie would stand there all the time helping them, they do it anyways, but you will notice just before they make the stroke, the caddie moves.

Just for fun, next time your playing a round and your buddy is tending the flag for you, dollars to donuts he will have one of his feet on the line behind the hole, people do it all the time. It will cost him a one stroke penalty...lol...some one will want to break out the rule book, any ways Rule 16 covers most of these
http://golf.about.com/cs/rulesofgolf/a/rule16.htm