Just spoke to Ticketmaster:
Write a letter to:
Jo Mead
Ticketing
AEG Live
25 Canada Street
Canary Wharf
London
E14 5LQ

In that letter you need to put the last 4 digits of your credit card, ticketmaster reference number, your home address, contact telephone number and 3 choices of dates you can make for an aftershow. I would mention refund if you can't make any future dates. Gotta be worth a try!
[Edited 8/15/07 11:47am]