This is one of those stories that are often told but there is a lack of credible evidence. This story is often attributed to Marshal Louis-Nicholas Davout, who was Colonel-General of the Imperial Grenadiers. The soldier in the story was capable of applying for the Guard and getting in with the exception of his height. Marshal Davout, in a very rare instance of rule breaking, told the soldier to put a pack of cards in his boots so he would have the extra inch. I would recommend John Elting's Swords Around A Throne which is packed with these little nuggets.