The entry period is very short for this one, with the ballot closing on 27th October.
The following link will take you to the National Lottery website where you will find details of a 5m race being organised around the Olympic Park next March and finishing in the Sports Stadium. Whilst some may consider it expensive at £15 for a 5m event, the once in a life time opportunity it presents may make you feel that as a one off it is worth the cost. The race finishes in the Olympic Stadium, and your entry fee includes 2 Olympic Stadium spectator tickets. There are only 5,000 places available via the ballot.
http://www.nationallotteryrun.com/TheEvent/AboutTheEvent.aspx