What I am posting back to you is the only things that come to mind right now without you tellng us if or what steps you may have already done.
First off - you've been there before [was it on a YMS visa?] & presumably have a National Insurance number.
You are also degreed, have worked an olympic event previousy & would think that you are still under 30
One suggestion - have you looked at & applied at the LOG website?
http://locogrecruitment.london2012.com/jobs/mainI would also like to suggest, considering you are after a specific work type - that you could try applying now for a temporary work visa - specific to & for the olympic event
You have not said whether you may also qualify for an ancestry visa?
http://www.ukba.homeoffice.gov.uk/visas ... -ancestry/
Disclaimer: I am not an immigration expert & anything that I post on visa & immigration is based soley on more than 30 years of personal experience & interaction with the UKBA & Home office.