WOW that is dedication!!
It may be possible (im just speculating, as I know Autographica does this) to pay and reserve your tickets, so you can collect them on the day, as long as you have a print out of your receipt. I'm sure someone else could advise you better than me though.
Haha, I have been planning a London trip for a while, although I have to admit, I did kind of plan my travel times around this just seemed convenient! Plus, I'm far too deep into the Whoniverse to miss a chance to see John Barrowman in the flesh.
I sent an email to Showmasters asking about it, so I'm just waiting for a reply from them :) hopefully it'll work out!!!