Santa Cruz is the first team I can find anything about doing it but it must have been done long before that.
It's a bit daft. For the number of goals that it would actually stop I think it's much more beneficial to have an extra man to deal with rebounds or wait in space for a potential counter. Plus by putting a man there you force the taker to try and put it over/round the wall which is probably a better option in the first place...
Suppose it means all the wall can and will jump, making it harder to go over the wall, especially useful for freekicks around the edge of the area where its hard to get it up and down in time anyway.
I'd like to see all 10 outfield players hanging off the crossbar like monkeys or Billy Casper and the keeper in a one man wall.
My tactic would be for all 10 outfield players to line up on the goal line, on tiptoe Billy Elliot style, in descending order of height from left to right. The goalkeeper would then stand at the right near the post waving his arms about. They'd never score, but there'd be some epic goalmouth scrambles.