Hi chicane,
I have been for an interview for LHR SH very recently (still don't know the outcome..).
During the presentation we have been told that if successful we'll be in a holding pool, however there should be courses late summer (to be precise from august or september onwards). So afterall you might not have to wait long....assuming that the holding poole is the same for who applied for LGW and LHR.
Good luck anyway