Pretty much as treadigraph said. They are towed away to allow other A380s to use the stands and are bought back when they are needed again.
Emirates and SQ send the A380 to LHR and also use T3 so the limited number of A380 capable gates are needed at various points throughout the day.
NZ, UA, JJ and LY all do the same at T1. Bring aircraft in, de-plane pax and then park them on remote stands until they are needed again.