When I did this last year I did the following:
Printed the application forms, filled out history since I was 18 including addresses when I was in USA and Canada. I provided a cell phone bill, bank statement and home insurance letter as proof of residence.
I sent the application, along with a postal order, photographs to my parents house.
They then took the photographs and part of the application that needed to be endorsed to a family friend in the UK.
My mum then posted the application to the police and the police sent my results 5 days later to me.
I hope that makes sense. If I were you I would just put in proof of your last address and leave it there and pretend you still live there.